From a1a2138b35c26c0bfd4fa31223c8069f1a996268 Mon Sep 17 00:00:00 2001
From: Pavan Deolasee <pavan.deolasee@gmail.com>
Date: Tue, 27 Nov 2018 16:43:15 +0530
Subject: [PATCH] MERGE SQL Command following SQL:2016

    MERGE performs actions that modify rows in the target table
    using a source table or query. MERGE provides a single SQL
    statement that can conditionally INSERT/UPDATE/DELETE rows
    a task that would other require multiple PL statements.
    e.g.

    MERGE INTO target AS t
    USING source AS s
    ON t.tid = s.sid
    WHEN MATCHED AND t.balance > s.delta THEN
      UPDATE SET balance = t.balance - s.delta
    WHEN MATCHED THEN
      DELETE
    WHEN NOT MATCHED AND s.delta > 0 THEN
      INSERT VALUES (s.sid, s.delta)
    WHEN NOT MATCHED THEN
      DO NOTHING;

    MERGE works with regular and partitioned tables, including
    column and row security enforcement, as well as support for
    row, statement and transition triggers.

    MERGE is optimized for OLTP and is parameterizable, though
    also useful for large scale ETL/ELT. MERGE is not intended
    to be used in preference to existing single SQL commands
    for INSERT, UPDATE or DELETE since there is some overhead.
    MERGE can be used statically from PL/pgSQL.

    MERGE does not yet support inheritance, write rules,
    RETURNING clauses, updatable views or foreign tables.
    MERGE follows SQL Standard per the most recent SQL:2016.

    Includes full tests and documentation, including full
    isolation tests to demonstrate the concurrent behavior.

    This version written from scratch in 2017 by Simon Riggs,
	using docs and tests originally written in 2009. Later work
    from Pavan Deolasee has been both complex and deep, leaving
    the lead author credit now in his hands.
    Extensive discussion of concurrency from Peter Geoghegan,
    with thanks for the time and effort contributed.

    Various issues reported via sqlsmith by Andreas Seltenreich

    Authors: Pavan Deolasee, Simon Riggs
    Reviewer: Peter Geoghegan, Amit Langote, Tomas Vondra, Simon Riggs

    Discussion:
    https://postgr.es/m/CANP8+jKitBSrB7oTgT9CY2i1ObfOt36z0XMraQc+Xrz8QB0nXA@mail.gmail.com
    https://postgr.es/m/CAH2-WzkJdBuxj9PO=2QaO9-3h3xGbQPZ34kJH=HukRekwM-GZg@mail.gmail.com
---
 contrib/test_decoding/expected/ddl.out             |   46 +
 contrib/test_decoding/sql/ddl.sql                  |   16 +
 doc/src/sgml/libpq.sgml                            |    8 +-
 doc/src/sgml/mvcc.sgml                             |   28 +-
 doc/src/sgml/plpgsql.sgml                          |    3 +-
 doc/src/sgml/ref/allfiles.sgml                     |    1 +
 doc/src/sgml/ref/create_policy.sgml                |    7 +
 doc/src/sgml/ref/insert.sgml                       |   11 +-
 doc/src/sgml/ref/merge.sgml                        |  617 ++++++++
 doc/src/sgml/reference.sgml                        |    1 +
 doc/src/sgml/trigger.sgml                          |   20 +
 src/backend/access/heap/heapam.c                   |   28 +-
 src/backend/catalog/sql_features.txt               |    6 +-
 src/backend/commands/explain.c                     |   37 +-
 src/backend/commands/prepare.c                     |    1 +
 src/backend/commands/trigger.c                     |  262 +++-
 src/backend/executor/Makefile                      |    2 +-
 src/backend/executor/README                        |   11 +
 src/backend/executor/execMain.c                    |   17 +
 src/backend/executor/execMerge.c                   |  679 ++++++++
 src/backend/executor/execPartition.c               |  279 +++-
 src/backend/executor/execReplication.c             |    5 +-
 src/backend/executor/instrument.c                  |    4 +-
 src/backend/executor/nodeIndexonlyscan.c           |    2 +-
 src/backend/executor/nodeModifyTable.c             |  298 +++-
 src/backend/executor/spi.c                         |    3 +
 src/backend/nodes/copyfuncs.c                      |   58 +
 src/backend/nodes/equalfuncs.c                     |   49 +
 src/backend/nodes/nodeFuncs.c                      |   64 +-
 src/backend/nodes/outfuncs.c                       |   40 +
 src/backend/nodes/readfuncs.c                      |   45 +
 src/backend/optimizer/plan/createplan.c            |   20 +-
 src/backend/optimizer/plan/planner.c               |   29 +-
 src/backend/optimizer/plan/setrefs.c               |   54 +
 src/backend/optimizer/prep/preptlist.c             |   41 +
 src/backend/optimizer/util/pathnode.c              |   11 +-
 src/backend/optimizer/util/plancat.c               |    4 +
 src/backend/parser/Makefile                        |    2 +-
 src/backend/parser/analyze.c                       |   18 +-
 src/backend/parser/gram.y                          |  151 +-
 src/backend/parser/parse_agg.c                     |   10 +
 src/backend/parser/parse_clause.c                  |   57 +-
 src/backend/parser/parse_collate.c                 |    1 +
 src/backend/parser/parse_expr.c                    |    3 +
 src/backend/parser/parse_func.c                    |    3 +
 src/backend/parser/parse_merge.c                   |  654 ++++++++
 src/backend/parser/parse_relation.c                |   10 +
 src/backend/rewrite/rewriteHandler.c               |  115 +-
 src/backend/rewrite/rowsecurity.c                  |   97 ++
 src/backend/tcop/pquery.c                          |    5 +
 src/backend/tcop/utility.c                         |   16 +
 src/bin/psql/tab-complete.c                        |   79 +-
 src/include/access/heapam.h                        |   13 +-
 src/include/commands/trigger.h                     |    6 +-
 src/include/executor/execMerge.h                   |   31 +
 src/include/executor/execPartition.h               |    5 +
 src/include/executor/instrument.h                  |    5 +-
 src/include/executor/nodeModifyTable.h             |   24 +
 src/include/executor/spi.h                         |    1 +
 src/include/nodes/execnodes.h                      |   75 +-
 src/include/nodes/nodes.h                          |    7 +-
 src/include/nodes/parsenodes.h                     |   53 +-
 src/include/nodes/plannodes.h                      |    8 +-
 src/include/nodes/relation.h                       |    7 +-
 src/include/optimizer/pathnode.h                   |    7 +-
 src/include/parser/analyze.h                       |    5 +
 src/include/parser/kwlist.h                        |    2 +
 src/include/parser/parse_clause.h                  |    5 +-
 src/include/parser/parse_merge.h                   |   19 +
 src/include/parser/parse_node.h                    |    5 +-
 src/include/rewrite/rewriteHandler.h               |    1 +
 src/interfaces/libpq/fe-exec.c                     |    9 +-
 src/pl/plpgsql/src/pl_exec.c                       |    7 +-
 src/pl/plpgsql/src/pl_gram.y                       |    8 +
 src/pl/plpgsql/src/pl_scanner.c                    |    1 +
 src/pl/plpgsql/src/plpgsql.h                       |    4 +-
 src/test/isolation/expected/merge-delete.out       |   97 ++
 .../isolation/expected/merge-insert-update.out     |   84 +
 .../isolation/expected/merge-match-recheck.out     |  106 ++
 src/test/isolation/expected/merge-update.out       |  238 +++
 src/test/isolation/isolation_schedule              |    4 +
 src/test/isolation/specs/merge-delete.spec         |   51 +
 src/test/isolation/specs/merge-insert-update.spec  |   52 +
 src/test/isolation/specs/merge-match-recheck.spec  |   79 +
 src/test/isolation/specs/merge-update.spec         |  133 ++
 src/test/regress/expected/identity.out             |   55 +
 src/test/regress/expected/merge.out                | 1655 ++++++++++++++++++++
 src/test/regress/expected/privileges.out           |   98 ++
 src/test/regress/expected/rowsecurity.out          |  182 +++
 src/test/regress/expected/rules.out                |   31 +
 src/test/regress/expected/triggers.out             |   48 +
 src/test/regress/expected/with.out                 |  137 ++
 src/test/regress/parallel_schedule                 |    2 +-
 src/test/regress/serial_schedule                   |    1 +
 src/test/regress/sql/identity.sql                  |   45 +
 src/test/regress/sql/merge.sql                     | 1165 ++++++++++++++
 src/test/regress/sql/privileges.sql                |  108 ++
 src/test/regress/sql/rowsecurity.sql               |  156 ++
 src/test/regress/sql/rules.sql                     |   33 +
 src/test/regress/sql/triggers.sql                  |   47 +
 src/test/regress/sql/with.sql                      |   56 +
 src/tools/pgindent/typedefs.list                   |    3 +
 102 files changed, 8779 insertions(+), 223 deletions(-)
 create mode 100644 doc/src/sgml/ref/merge.sgml
 create mode 100644 src/backend/executor/execMerge.c
 create mode 100644 src/backend/parser/parse_merge.c
 create mode 100644 src/include/executor/execMerge.h
 create mode 100644 src/include/parser/parse_merge.h
 create mode 100644 src/test/isolation/expected/merge-delete.out
 create mode 100644 src/test/isolation/expected/merge-insert-update.out
 create mode 100644 src/test/isolation/expected/merge-match-recheck.out
 create mode 100644 src/test/isolation/expected/merge-update.out
 create mode 100644 src/test/isolation/specs/merge-delete.spec
 create mode 100644 src/test/isolation/specs/merge-insert-update.spec
 create mode 100644 src/test/isolation/specs/merge-match-recheck.spec
 create mode 100644 src/test/isolation/specs/merge-update.spec
 create mode 100644 src/test/regress/expected/merge.out
 create mode 100644 src/test/regress/sql/merge.sql

diff --git a/contrib/test_decoding/expected/ddl.out b/contrib/test_decoding/expected/ddl.out
index b7c76469fc..79c359d6e3 100644
--- a/contrib/test_decoding/expected/ddl.out
+++ b/contrib/test_decoding/expected/ddl.out
@@ -192,6 +192,52 @@ SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'inc
  COMMIT
 (33 rows)
 
+-- MERGE support
+BEGIN;
+MERGE INTO replication_example t
+	USING (SELECT i as id, i as data, i as num FROM generate_series(-20, 5) i) s
+	ON t.id = s.id
+	WHEN MATCHED AND t.id < 0 THEN
+		UPDATE SET somenum = somenum + 1
+	WHEN MATCHED AND t.id >= 0 THEN
+		DELETE
+	WHEN NOT MATCHED THEN
+		INSERT VALUES (s.*);
+COMMIT;
+/* display results */
+SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1');
+                                                                       data                                                                       
+--------------------------------------------------------------------------------------------------------------------------------------------------
+ BEGIN
+ table public.replication_example: INSERT: id[integer]:-20 somedata[integer]:-20 somenum[integer]:-20 zaphod1[integer]:null zaphod2[integer]:null
+ table public.replication_example: INSERT: id[integer]:-19 somedata[integer]:-19 somenum[integer]:-19 zaphod1[integer]:null zaphod2[integer]:null
+ table public.replication_example: INSERT: id[integer]:-18 somedata[integer]:-18 somenum[integer]:-18 zaphod1[integer]:null zaphod2[integer]:null
+ table public.replication_example: INSERT: id[integer]:-17 somedata[integer]:-17 somenum[integer]:-17 zaphod1[integer]:null zaphod2[integer]:null
+ table public.replication_example: INSERT: id[integer]:-16 somedata[integer]:-16 somenum[integer]:-16 zaphod1[integer]:null zaphod2[integer]:null
+ table public.replication_example: UPDATE: id[integer]:-15 somedata[integer]:-15 somenum[integer]:-14 zaphod1[integer]:null zaphod2[integer]:null
+ table public.replication_example: UPDATE: id[integer]:-14 somedata[integer]:-14 somenum[integer]:-13 zaphod1[integer]:null zaphod2[integer]:null
+ table public.replication_example: UPDATE: id[integer]:-13 somedata[integer]:-13 somenum[integer]:-12 zaphod1[integer]:null zaphod2[integer]:null
+ table public.replication_example: UPDATE: id[integer]:-12 somedata[integer]:-12 somenum[integer]:-11 zaphod1[integer]:null zaphod2[integer]:null
+ table public.replication_example: UPDATE: id[integer]:-11 somedata[integer]:-11 somenum[integer]:-10 zaphod1[integer]:null zaphod2[integer]:null
+ table public.replication_example: UPDATE: id[integer]:-10 somedata[integer]:-10 somenum[integer]:-9 zaphod1[integer]:null zaphod2[integer]:null
+ table public.replication_example: UPDATE: id[integer]:-9 somedata[integer]:-9 somenum[integer]:-8 zaphod1[integer]:null zaphod2[integer]:null
+ table public.replication_example: UPDATE: id[integer]:-8 somedata[integer]:-8 somenum[integer]:-7 zaphod1[integer]:null zaphod2[integer]:null
+ table public.replication_example: UPDATE: id[integer]:-7 somedata[integer]:-7 somenum[integer]:-6 zaphod1[integer]:null zaphod2[integer]:null
+ table public.replication_example: UPDATE: id[integer]:-6 somedata[integer]:-6 somenum[integer]:-5 zaphod1[integer]:null zaphod2[integer]:null
+ table public.replication_example: UPDATE: id[integer]:-5 somedata[integer]:-5 somenum[integer]:-4 zaphod1[integer]:null zaphod2[integer]:null
+ table public.replication_example: UPDATE: id[integer]:-4 somedata[integer]:-4 somenum[integer]:-3 zaphod1[integer]:null zaphod2[integer]:null
+ table public.replication_example: UPDATE: id[integer]:-3 somedata[integer]:-3 somenum[integer]:-2 zaphod1[integer]:null zaphod2[integer]:null
+ table public.replication_example: UPDATE: id[integer]:-2 somedata[integer]:-2 somenum[integer]:-1 zaphod1[integer]:null zaphod2[integer]:null
+ table public.replication_example: UPDATE: id[integer]:-1 somedata[integer]:-1 somenum[integer]:0 zaphod1[integer]:null zaphod2[integer]:null
+ table public.replication_example: DELETE: id[integer]:0
+ table public.replication_example: DELETE: id[integer]:1
+ table public.replication_example: DELETE: id[integer]:2
+ table public.replication_example: DELETE: id[integer]:3
+ table public.replication_example: DELETE: id[integer]:4
+ table public.replication_example: DELETE: id[integer]:5
+ COMMIT
+(28 rows)
+
 CREATE TABLE tr_unique(id2 serial unique NOT NULL, data int);
 INSERT INTO tr_unique(data) VALUES(10);
 ALTER TABLE tr_unique RENAME TO tr_pkey;
diff --git a/contrib/test_decoding/sql/ddl.sql b/contrib/test_decoding/sql/ddl.sql
index c4b10a4cf9..0e608b252f 100644
--- a/contrib/test_decoding/sql/ddl.sql
+++ b/contrib/test_decoding/sql/ddl.sql
@@ -93,6 +93,22 @@ COMMIT;
 /* display results */
 SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1');
 
+-- MERGE support
+BEGIN;
+MERGE INTO replication_example t
+	USING (SELECT i as id, i as data, i as num FROM generate_series(-20, 5) i) s
+	ON t.id = s.id
+	WHEN MATCHED AND t.id < 0 THEN
+		UPDATE SET somenum = somenum + 1
+	WHEN MATCHED AND t.id >= 0 THEN
+		DELETE
+	WHEN NOT MATCHED THEN
+		INSERT VALUES (s.*);
+COMMIT;
+
+/* display results */
+SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1');
+
 CREATE TABLE tr_unique(id2 serial unique NOT NULL, data int);
 INSERT INTO tr_unique(data) VALUES(10);
 ALTER TABLE tr_unique RENAME TO tr_pkey;
diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index d2e5b08541..38303c0262 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -3954,9 +3954,11 @@ char *PQcmdTuples(PGresult *res);
        <structname>PGresult</structname>. This function can only be used following
        the execution of a <command>SELECT</command>, <command>CREATE TABLE AS</command>,
        <command>INSERT</command>, <command>UPDATE</command>, <command>DELETE</command>,
-       <command>MOVE</command>, <command>FETCH</command>, or <command>COPY</command> statement,
-       or an <command>EXECUTE</command> of a prepared query that contains an
-       <command>INSERT</command>, <command>UPDATE</command>, or <command>DELETE</command> statement.
+       <command>MERGE</command>, <command>MOVE</command>, <command>FETCH</command>,
+       or <command>COPY</command> statement, or an <command>EXECUTE</command> of a
+       prepared query that contains an <command>INSERT</command>,
+       <command>UPDATE</command>, <command>DELETE</command>
+       or <command>MERGE</command> statement.
        If the command that generated the <structname>PGresult</structname> was anything
        else, <function>PQcmdTuples</function> returns an empty string. The caller
        should not free the return value directly. It will be freed when
diff --git a/doc/src/sgml/mvcc.sgml b/doc/src/sgml/mvcc.sgml
index bedd9a008d..4cd0465da1 100644
--- a/doc/src/sgml/mvcc.sgml
+++ b/doc/src/sgml/mvcc.sgml
@@ -422,6 +422,31 @@ COMMIT;
     <literal>11</literal>, which no longer matches the criteria.
    </para>
 
+   <para>
+    The <command>MERGE</command> allows the user to specify various combinations
+    of <command>INSERT</command>, <command>UPDATE</command> or
+    <command>DELETE</command> subcommands. A <command>MERGE</command> command
+    with both <command>INSERT</command> and <command>UPDATE</command>
+    subcommands looks similar to <command>INSERT</command> with an
+    <literal>ON CONFLICT DO UPDATE</literal> clause but does not guarantee
+    that either <command>INSERT</command> and <command>UPDATE</command> will occur.
+
+    If MERGE attempts an UPDATE or DELETE and the row is concurrently updated
+    but the join condition still passes for the current target and the current
+    source tuple, then MERGE will behave the same as the UPDATE or DELETE commands
+    and perform its action on the latest version of the row, using standard
+    EvalPlanQual. MERGE actions can be conditional, so conditions must be
+    re-evaluated on the latest row, starting from the first action.
+
+    On the other hand, if the row is concurrently updated or deleted so that
+    the join condition fails, then MERGE will execute a NOT MATCHED action, if it
+    exists and the AND WHEN qual evaluates to true.
+
+    If MERGE attempts an INSERT and a unique index is present and a duplicate
+    row is concurrently inserted then a uniqueness violation is raised. MERGE
+    does not attempt to avoid the ERROR by attempting an UPDATE.
+   </para>
+
    <para>
     Because Read Committed mode starts each command with a new snapshot
     that includes all transactions committed up to that instant,
@@ -900,7 +925,8 @@ ERROR:  could not serialize access due to read/write dependencies among transact
 
         <para>
          The commands <command>UPDATE</command>,
-         <command>DELETE</command>, and <command>INSERT</command>
+         <command>DELETE</command>, <command>INSERT</command> and
+         <command>MERGE</command>
          acquire this lock mode on the target table (in addition to
          <literal>ACCESS SHARE</literal> locks on any other referenced
          tables).  In general, this lock mode will be acquired by any
diff --git a/doc/src/sgml/plpgsql.sgml b/doc/src/sgml/plpgsql.sgml
index b9eb98cfd7..508566acec 100644
--- a/doc/src/sgml/plpgsql.sgml
+++ b/doc/src/sgml/plpgsql.sgml
@@ -1245,7 +1245,7 @@ EXECUTE format('SELECT count(*) FROM %I '
 </programlisting>
      Another restriction on parameter symbols is that they only work in
      <command>SELECT</command>, <command>INSERT</command>, <command>UPDATE</command>, and
-     <command>DELETE</command> commands.  In other statement
+     <command>DELETE</command> and <command>MERGE</command> commands.  In other statement
      types (generically called utility statements), you must insert
      values textually even if they are just data values.
     </para>
@@ -1520,6 +1520,7 @@ GET DIAGNOSTICS integer_var = ROW_COUNT;
           <listitem>
            <para>
             <command>UPDATE</command>, <command>INSERT</command>, and <command>DELETE</command>
+            and <command>MERGE</command>
             statements set <literal>FOUND</literal> true if at least one
             row is affected, false if no row is affected.
            </para>
diff --git a/doc/src/sgml/ref/allfiles.sgml b/doc/src/sgml/ref/allfiles.sgml
index c81c87ef41..7cd6ee85dc 100644
--- a/doc/src/sgml/ref/allfiles.sgml
+++ b/doc/src/sgml/ref/allfiles.sgml
@@ -159,6 +159,7 @@ Complete list of usable sgml source files in this directory.
 <!ENTITY load               SYSTEM "load.sgml">
 <!ENTITY lock               SYSTEM "lock.sgml">
 <!ENTITY move               SYSTEM "move.sgml">
+<!ENTITY merge              SYSTEM "merge.sgml">
 <!ENTITY notify             SYSTEM "notify.sgml">
 <!ENTITY prepare            SYSTEM "prepare.sgml">
 <!ENTITY prepareTransaction SYSTEM "prepare_transaction.sgml">
diff --git a/doc/src/sgml/ref/create_policy.sgml b/doc/src/sgml/ref/create_policy.sgml
index 2e1229c4f9..618dd45240 100644
--- a/doc/src/sgml/ref/create_policy.sgml
+++ b/doc/src/sgml/ref/create_policy.sgml
@@ -94,6 +94,13 @@ CREATE POLICY <replaceable class="parameter">name</replaceable> ON <replaceable
    exist, a <quote>default deny</quote> policy is assumed, so that no rows will
    be visible or updatable.
   </para>
+
+  <para>
+   No separate policy exists for <command>MERGE</command>. Instead policies
+   defined for <literal>SELECT</literal>, <literal>INSERT</literal>,
+   <literal>UPDATE</literal> and <literal>DELETE</literal> are applied
+   while executing MERGE, depending on the actions that are activated.
+  </para>
  </refsect1>
 
  <refsect1>
diff --git a/doc/src/sgml/ref/insert.sgml b/doc/src/sgml/ref/insert.sgml
index 62e142fd8e..da294aaa46 100644
--- a/doc/src/sgml/ref/insert.sgml
+++ b/doc/src/sgml/ref/insert.sgml
@@ -579,6 +579,13 @@ INSERT <replaceable>oid</replaceable> <replaceable class="parameter">count</repl
    is a partition, an error will occur if one of the input rows violates
    the partition constraint.
   </para>
+
+  <para>
+   You may also wish to consider using <command>MERGE</command>, since that
+   allows mixed <command>INSERT</command>, <command>UPDATE</command> and
+   <command>DELETE</command> within a single statement.
+   See <xref linkend="sql-merge"/>.
+  </para>
  </refsect1>
 
  <refsect1>
@@ -749,7 +756,9 @@ INSERT INTO distributors (did, dname) VALUES (10, 'Conrad International')
    Also, the case in
    which a column name list is omitted, but not all the columns are
    filled from the <literal>VALUES</literal> clause or <replaceable>query</replaceable>,
-   is disallowed by the standard.
+   is disallowed by the standard. If you prefer a more SQL Standard
+   conforming statement than <literal>ON CONFLICT</literal>, see
+   <xref linkend="sql-merge"/>.
   </para>
 
   <para>
diff --git a/doc/src/sgml/ref/merge.sgml b/doc/src/sgml/ref/merge.sgml
new file mode 100644
index 0000000000..b2a9f67cfa
--- /dev/null
+++ b/doc/src/sgml/ref/merge.sgml
@@ -0,0 +1,617 @@
+<!--
+doc/src/sgml/ref/merge.sgml
+PostgreSQL documentation
+-->
+
+<refentry id="sql-merge">
+
+ <refmeta>
+  <refentrytitle>MERGE</refentrytitle>
+  <manvolnum>7</manvolnum>
+  <refmiscinfo>SQL - Language Statements</refmiscinfo>
+ </refmeta>
+
+ <refnamediv>
+  <refname>MERGE</refname>
+  <refpurpose>insert, update, or delete rows of a table based upon source data</refpurpose>
+ </refnamediv>
+
+ <refsynopsisdiv>
+<synopsis>
+[ WITH <replaceable class="parameter">with_query</replaceable> [, ...] ]
+MERGE INTO <replaceable class="parameter">target_table_name</replaceable> [ [ AS ] <replaceable class="parameter">target_alias</replaceable> ]
+USING <replaceable class="parameter">data_source</replaceable>
+ON <replaceable class="parameter">join_condition</replaceable>
+<replaceable class="parameter">when_clause</replaceable> [...]
+
+where <replaceable class="parameter">data_source</replaceable> is
+
+{ <replaceable class="parameter">source_table_name</replaceable> |
+  ( source_query )
+}
+[ [ AS ] <replaceable class="parameter">source_alias</replaceable> ]
+
+and <replaceable class="parameter">when_clause</replaceable> is
+
+{ WHEN MATCHED [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_update</replaceable> | <replaceable class="parameter">merge_delete</replaceable> } |
+  WHEN NOT MATCHED [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_insert</replaceable> | DO NOTHING }
+}
+
+and <replaceable class="parameter">merge_insert</replaceable> is
+
+INSERT [( <replaceable class="parameter">column_name</replaceable> [, ...] )]
+[ OVERRIDING { SYSTEM | USER } VALUE ]
+{ VALUES ( { <replaceable class="parameter">expression</replaceable> | DEFAULT } [, ...] ) | DEFAULT VALUES }
+
+and <replaceable class="parameter">merge_update</replaceable> is
+
+UPDATE SET { <replaceable class="parameter">column_name</replaceable> = { <replaceable class="parameter">expression</replaceable> | DEFAULT } |
+             ( <replaceable class="parameter">column_name</replaceable> [, ...] ) = ( { <replaceable class="parameter">expression</replaceable> | DEFAULT } [, ...] )
+           } [, ...]
+
+and <replaceable class="parameter">merge_delete</replaceable> is
+
+DELETE
+</synopsis>
+ </refsynopsisdiv>
+
+ <refsect1>
+  <title>Description</title>
+
+  <para>
+   <command>MERGE</command> performs actions that modify rows in the
+   <replaceable class="parameter">target_table_name</replaceable>,
+   using the <replaceable class="parameter">data_source</replaceable>.
+   <command>MERGE</command> provides a single <acronym>SQL</acronym>
+   statement that can conditionally <command>INSERT</command>,
+   <command>UPDATE</command> or <command>DELETE</command> rows, a task
+   that would otherwise require multiple procedural language statements.
+  </para>
+
+  <para>
+   First, the <command>MERGE</command> command performs a join
+   from <replaceable class="parameter">data_source</replaceable> to
+   <replaceable class="parameter">target_table_name</replaceable>
+   producing zero or more candidate change rows.  For each candidate change
+   row the status of <literal>MATCHED</literal> or <literal>NOT MATCHED</literal> is set
+   just once, after which <literal>WHEN</literal> clauses are evaluated
+   in the order specified. If one of them is activated, the specified
+   action occurs. No more than one <literal>WHEN</literal> clause can be
+   activated for any candidate change row.  
+  </para>
+
+  <para>
+   <command>MERGE</command> actions have the same effect as
+   regular <command>UPDATE</command>, <command>INSERT</command>, or
+   <command>DELETE</command> commands of the same names. The syntax of
+   those commands is different, notably that there is no <literal>WHERE</literal>
+   clause and no tablename is specified.  All actions refer to the
+   <replaceable class="parameter">target_table_name</replaceable>,
+   though modifications to other tables may be made using triggers.
+  </para>
+
+  <para>
+   When <literal>DO NOTHING</literal> action is specified, the source row is
+   skipped. Since actions are evaluated in the given order, <literal>DO
+   NOTHING</literal> can be handy to skip non-interesting source rows before
+   more fine-grained handling.
+  </para>
+
+  <para>
+   There is no MERGE privilege.  
+   You must have the <literal>UPDATE</literal> privilege on the column(s)
+   of the <replaceable class="parameter">target_table_name</replaceable>
+   referred to in the <literal>SET</literal> clause
+   if you specify an update action, the <literal>INSERT</literal> privilege
+   on the <replaceable class="parameter">target_table_name</replaceable>
+   if you specify an insert action and/or the <literal>DELETE</literal>
+   privilege on the <replaceable class="parameter">target_table_name</replaceable>
+   if you specify a delete action on the
+   <replaceable class="parameter">target_table_name</replaceable>.
+   Privileges are tested once at statement start and are checked
+   whether or not particular <literal>WHEN</literal> clauses are activated
+   during the subsequent execution.
+   You will require the <literal>SELECT</literal> privilege on the
+   <replaceable class="parameter">data_source</replaceable> and any column(s)
+   of the <replaceable class="parameter">target_table_name</replaceable>
+   referred to in a <literal>condition</literal>.
+  </para>
+
+  <para>
+   MERGE is not supported if the <replaceable
+   class="parameter">target_table_name</replaceable> has
+   <literal>RULES</literal> defined on it.
+   See <xref linkend="rules"/> for more information about <literal>RULES</literal>.
+  </para>
+ </refsect1>
+
+ <refsect1>
+  <title>Parameters</title>
+
+  <variablelist>
+   <varlistentry>
+    <term><replaceable class="parameter">target_table_name</replaceable></term>
+    <listitem>
+     <para>
+      The name (optionally schema-qualified) of the target table to merge into.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term><replaceable class="parameter">target_alias</replaceable></term>
+    <listitem>
+     <para>
+      A substitute name for the target table. When an alias is
+      provided, it completely hides the actual name of the table.  For
+      example, given <literal>MERGE foo AS f</literal>, the remainder of the
+      <command>MERGE</command> statement must refer to this table as
+      <literal>f</literal> not <literal>foo</literal>.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term><replaceable class="parameter">source_table_name</replaceable></term>
+    <listitem>
+     <para>
+      The name (optionally schema-qualified) of the source table, view or
+      transition table.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term><replaceable class="parameter">source_query</replaceable></term>
+    <listitem>
+     <para>
+      A query (<command>SELECT</command> statement or <command>VALUES</command>
+      statement) that supplies the rows to be merged into the
+      <replaceable class="parameter">target_table_name</replaceable>.
+      Refer to the <xref linkend="sql-select"/>
+      statement or <xref linkend="sql-values"/>
+      statement for a description of the syntax.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term><replaceable class="parameter">source_alias</replaceable></term>
+    <listitem>
+     <para>
+      A substitute name for the data source. When an alias is
+      provided, it completely hides whether table or query was specified.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term><replaceable class="parameter">join_condition</replaceable></term>
+    <listitem>
+     <para>
+      <replaceable class="parameter">join_condition</replaceable> is
+      an expression resulting in a value of type
+      <type>boolean</type> (similar to a <literal>WHERE</literal>
+      clause) that specifies which rows in the 
+      <replaceable class="parameter">data_source</replaceable>
+      match rows in the
+      <replaceable class="parameter">target_table_name</replaceable>.
+     </para>
+     <warning>
+      <para>
+       Only columns from <replaceable class="parameter">target_table_name</replaceable>
+       that attempt to match <replaceable class="parameter">data_source</replaceable>
+       rows should appear in <replaceable class="parameter">join_condition</replaceable>.
+       <replaceable class="parameter">join_condition</replaceable> subexpressions that
+       only reference <replaceable class="parameter">target_table_name</replaceable>
+       columns can only affect which action is taken, often in surprising ways.
+      </para>
+     </warning>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term><replaceable class="parameter">when_clause</replaceable></term>
+    <listitem>
+     <para>
+      At least one <literal>WHEN</literal> clause is required.
+     </para>
+     <para>
+      If the <literal>WHEN</literal> clause specifies <literal>WHEN MATCHED</literal>
+      and the candidate change row matches a row in the
+      <replaceable class="parameter">target_table_name</replaceable>
+      the <literal>WHEN</literal> clause is activated if the
+      <replaceable class="parameter">condition</replaceable> is
+      absent or is present and evaluates to <literal>true</literal>.
+      If the <literal>WHEN</literal> clause specifies <literal>WHEN NOT MATCHED</literal>
+      and the candidate change row does not match a row in the
+      <replaceable class="parameter">target_table_name</replaceable>
+      the <literal>WHEN</literal> clause is activated if the
+      <replaceable class="parameter">condition</replaceable> is
+      absent or is present and evaluates to <literal>true</literal>.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term><replaceable class="parameter">condition</replaceable></term>
+    <listitem>
+     <para>
+      An expression that returns a value of type <type>boolean</type>.
+      If this expression returns <literal>true</literal> then the <literal>WHEN</literal>
+      clause will be activated and the corresponding action will occur for
+      that row. The expression may not contain functions that possibly performs
+      writes to the database.
+     </para>
+     <para>
+      A condition on a <literal>WHEN MATCHED</literal> clause can refer to columns
+      in both the source and the target relation. A condition on a
+      <literal>WHEN NOT MATCHED</literal> clause can only refer to columns from
+      the source relation, since by definition there is no matching target row.
+      Only the system attributes from the target table are accessible.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term><replaceable class="parameter">merge_insert</replaceable></term>
+    <listitem>
+     <para>
+      The specification of an <literal>INSERT</literal> action that inserts
+      one row into the target table.
+      The target column names can be listed in any order. If no list of
+      column names is given at all, the default is all the columns of the
+      table in their declared order.
+     </para>
+     <para>
+      Each column not present in the explicit or implicit column list will be
+      filled with a default value, either its declared default value
+      or null if there is none.
+     </para>
+     <para>
+      If the expression for any column is not of the correct data type,
+      automatic type conversion will be attempted.
+     </para>
+     <para>
+      If <replaceable class="parameter">target_table_name</replaceable>
+      is a partitioned table, each row is routed to the appropriate partition
+      and inserted into it.
+      If <replaceable class="parameter">target_table_name</replaceable>
+      is a partition, an error will occur if one of the input rows violates
+      the partition constraint.
+     </para>
+     <para>
+      Column names may not be specified more than once.
+      <command>INSERT</command> actions cannot contain sub-selects. 
+     </para>
+     <para>
+      Only one <literal>VALUES</literal> clause can be specified.
+      The <literal>VALUES</literal> clause can only refer to columns from
+      the source relation, since by definition there is no matching target row.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term><replaceable class="parameter">merge_update</replaceable></term>
+    <listitem>
+     <para>
+      The specification of an <literal>UPDATE</literal> action that updates
+      the current row of the <replaceable
+      class="parameter">target_table_name</replaceable>.
+      Column names may not be specified more than once.
+     </para>
+     <para>
+      Do not include the table name, as you would normally do with an
+      <xref linkend="sql-update"/> command.
+      For example, <literal>UPDATE tab SET col = 1</literal> is invalid. Also,
+      do not include a <literal>WHERE</literal> clause, since only the current
+      row can be updated. For example,
+      <literal>UPDATE SET col = 1 WHERE key = 57</literal> is invalid.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term><replaceable class="parameter">merge_delete</replaceable></term>
+    <listitem>
+     <para>
+      Specifies a <literal>DELETE</literal> action that deletes the current row
+      of the <replaceable class="parameter">target_table_name</replaceable>.
+      Do not include the tablename or any other clauses, as you would normally
+      do with an <xref linkend="sql-delete"/> command.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term><replaceable class="parameter">column_name</replaceable></term>
+    <listitem>
+     <para>
+      The name of a column in the <replaceable
+      class="parameter">target_table_name</replaceable>.  The column name
+      can be qualified with a subfield name or array subscript, if
+      needed.  (Inserting into only some fields of a composite
+      column leaves the other fields null.)  When referencing a
+      column, do not include the table's name in the specification
+      of a target column.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term><literal>OVERRIDING SYSTEM VALUE</literal></term>
+    <listitem>
+     <para>
+      Without this clause, it is an error to specify an explicit value
+      (other than <literal>DEFAULT</literal>) for an identity column defined
+      as <literal>GENERATED ALWAYS</literal>.  This clause overrides that
+      restriction.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term><literal>OVERRIDING USER VALUE</literal></term>
+    <listitem>
+     <para>
+      If this clause is specified, then any values supplied for identity
+      columns defined as <literal>GENERATED BY DEFAULT</literal> are ignored
+      and the default sequence-generated values are applied.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term><literal>DEFAULT VALUES</literal></term>
+    <listitem>
+     <para>
+      All columns will be filled with their default values.
+      (An <literal>OVERRIDING</literal> clause is not permitted in this
+      form.)
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term><replaceable class="parameter">expression</replaceable></term>
+    <listitem>
+     <para>
+      An expression to assign to the column.  The expression can use the
+      old values of this and other columns in the table.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term><literal>DEFAULT</literal></term>
+    <listitem>
+     <para>
+      Set the column to its default value (which will be NULL if no
+      specific default expression has been assigned to it).
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term><replaceable class="parameter">with_query</replaceable></term>
+    <listitem>
+     <para>
+      The <literal>WITH</literal> clause allows you to specify one or more
+      subqueries that can be referenced by name in the <command>MERGE</command>
+      query. See <xref linkend="queries-with"/> and <xref linkend="sql-select"/>
+      for details.
+     </para>
+    </listitem>
+   </varlistentry>
+
+  </variablelist>
+ </refsect1>
+
+ <refsect1>
+  <title>Outputs</title>
+
+  <para>
+   On successful completion, a <command>MERGE</command> command returns a command
+   tag of the form
+<screen>
+MERGE <replaceable class="parameter">total-count</replaceable>
+</screen>
+   The <replaceable class="parameter">total-count</replaceable> is the total
+   number of rows changed (whether inserted, updated, or deleted).
+   If <replaceable class="parameter">total-count</replaceable> is 0, no rows
+   were changed in any way.
+  </para>
+
+ </refsect1>
+
+ <refsect1>
+  <title>Execution</title>
+
+  <para>
+   The following steps take place during the execution of
+   <command>MERGE</command>.
+    <orderedlist>
+     <listitem>
+      <para>
+       Perform any BEFORE STATEMENT triggers for all actions specified, whether or
+       not their <literal>WHEN</literal> clauses are activated during execution.
+      </para>
+     </listitem>
+     <listitem>
+      <para>
+       Perform a join from source to target table.
+       The resulting query will be optimized normally and will produce
+       a set of candidate change row. For each candidate change row
+       <orderedlist>
+        <listitem>
+         <para>
+          Evaluate whether each row is MATCHED or NOT MATCHED.
+         </para>
+        </listitem>
+        <listitem>
+         <para>
+          Test each WHEN condition in the order specified until one activates.
+         </para>
+        </listitem>
+        <listitem>
+         <para>
+          When activated, perform the following actions
+          <orderedlist>
+           <listitem>
+            <para>
+             Perform any BEFORE ROW triggers that fire for the action's event type.
+            </para>
+           </listitem>
+           <listitem>
+            <para>
+             Apply the action specified, invoking any check constraints on the
+             target table.
+             However, it will not invoke rules.
+            </para>
+           </listitem>
+           <listitem>
+            <para>
+             Perform any AFTER ROW triggers that fire for the action's event type.
+            </para>
+           </listitem>
+          </orderedlist>
+         </para>
+        </listitem>
+       </orderedlist>
+      </para>
+     </listitem>
+     <listitem>
+      <para>
+       Perform any AFTER STATEMENT triggers for actions specified, whether or
+       not they actually occur.  This is similar to the behavior of an
+       <command>UPDATE</command> statement that modifies no rows.
+      </para>
+     </listitem>
+    </orderedlist>
+   In summary, statement triggers for an event type (say, INSERT) will
+   be fired whenever we <emphasis>specify</emphasis> an action of that kind. Row-level
+   triggers will fire only for the one event type <emphasis>activated</emphasis>.
+   So a <command>MERGE</command> might fire statement triggers for both
+   <command>UPDATE</command> and <command>INSERT</command>, even though only
+   <command>UPDATE</command> row triggers were fired.
+  </para>
+
+  <para>
+   You should ensure that the join produces at most one candidate change row
+   for each target row.  In other words, a target row shouldn't join to more
+   than one data source row.  If it does, then only one of the candidate change
+   rows will be used to modify the target row, later attempts to modify will
+   cause an error.  This can also occur if row triggers make changes to the
+   target table which are then subsequently modified by <command>MERGE</command>.
+   If the repeated action is an <command>INSERT</command> this will
+   cause a uniqueness violation while a repeated <command>UPDATE</command> or
+   <command>DELETE</command> will cause a cardinality violation; the latter behavior
+   is required by the <acronym>SQL</acronym> Standard. This differs from
+   historical <productname>PostgreSQL</productname> behavior of joins in
+   <command>UPDATE</command> and <command>DELETE</command> statements where second and
+   subsequent attempts to modify are simply ignored.
+  </para>
+
+  <para>
+   If a <literal>WHEN</literal> clause omits an <literal>AND</literal> clause it becomes
+   the final reachable clause of that kind (<literal>MATCHED</literal> or
+   <literal>NOT MATCHED</literal>). If a later <literal>WHEN</literal> clause of that kind
+   is specified it would be provably unreachable and an error is raised.
+   If a final reachable clause is omitted it is possible that no action
+   will be taken for a candidate change row.
+  </para>
+
+ </refsect1>
+ <refsect1>
+  <title>Notes</title>
+
+  <para>
+   The order in which rows are generated from the data source is indeterminate
+   by default. A <replaceable class="parameter">source_query</replaceable>
+   can be used to specify a consistent ordering, if required, which might be
+   needed to avoid deadlocks between concurrent transactions.
+  </para>
+
+  <para>
+   There is no <literal>RETURNING</literal> clause with <command>MERGE</command>.
+   Actions of <command>INSERT</command>, <command>UPDATE</command> and <command>DELETE</command>
+   cannot contain <literal>RETURNING</literal> or <literal>WITH</literal> clauses.
+  </para>
+
+  <tip>
+   <para>
+    You may also wish to consider using <command>INSERT ... ON CONFLICT</command> as an
+    alternative statement which offers the ability to run an <command>UPDATE</command>
+    if a concurrent <command>INSERT</command> occurs.  There are a variety of
+    differences and restrictions between the two statement types and they are not
+    interchangeable.
+   </para>
+  </tip>
+ </refsect1>
+
+ <refsect1>
+  <title>Examples</title>
+
+  <para>
+   Perform maintenance on CustomerAccounts based upon new Transactions.
+
+<programlisting>
+MERGE CustomerAccount CA
+USING RecentTransactions T
+ON T.CustomerId = CA.CustomerId
+WHEN MATCHED THEN
+  UPDATE SET Balance = Balance + TransactionValue
+WHEN NOT MATCHED THEN
+  INSERT (CustomerId, Balance)
+  VALUES (T.CustomerId, T.TransactionValue);
+</programlisting>
+
+   notice that this would be exactly equivalent to the following
+   statement because the <literal>MATCHED</literal> result does not change
+   during execution
+
+<programlisting>
+MERGE CustomerAccount CA
+USING (Select CustomerId, TransactionValue From RecentTransactions) AS T
+ON CA.CustomerId = T.CustomerId
+WHEN NOT MATCHED THEN
+  INSERT (CustomerId, Balance)
+  VALUES (T.CustomerId, T.TransactionValue)
+WHEN MATCHED THEN
+  UPDATE SET Balance = Balance + TransactionValue;
+</programlisting>
+  </para>
+
+  <para>
+   Attempt to insert a new stock item along with the quantity of stock. If
+   the item already exists, instead update the stock count of the existing
+   item. Don't allow entries that have zero stock.
+<programlisting>
+MERGE INTO wines w
+USING wine_stock_changes s
+ON s.winename = w.winename
+WHEN NOT MATCHED AND s.stock_delta > 0 THEN
+  INSERT VALUES(s.winename, s.stock_delta)
+WHEN MATCHED AND w.stock + s.stock_delta > 0 THEN
+  UPDATE SET stock = w.stock + s.stock_delta;
+WHEN MATCHED THEN
+  DELETE;
+</programlisting>
+
+   The wine_stock_changes table might be, for example, a temporary table
+   recently loaded into the database.
+  </para>
+
+ </refsect1>
+
+ <refsect1>
+  <title>Compatibility</title>
+   <para>
+    This command conforms to the <acronym>SQL</acronym> standard.
+  </para>
+   <para>
+    The WITH clause and DO NOTHING action are extensions to the <acronym>SQL</acronym> standard.
+  </para>
+ </refsect1>
+</refentry>
diff --git a/doc/src/sgml/reference.sgml b/doc/src/sgml/reference.sgml
index db4f4167e3..78c214f1b0 100644
--- a/doc/src/sgml/reference.sgml
+++ b/doc/src/sgml/reference.sgml
@@ -186,6 +186,7 @@
    &listen;
    &load;
    &lock;
+   &merge;
    &move;
    &notify;
    &prepare;
diff --git a/doc/src/sgml/trigger.sgml b/doc/src/sgml/trigger.sgml
index be9c228448..efb6506932 100644
--- a/doc/src/sgml/trigger.sgml
+++ b/doc/src/sgml/trigger.sgml
@@ -182,6 +182,26 @@
     will be fired.
    </para>
 
+   <para>
+    No separate triggers are defined for <command>MERGE</command>. Instead,
+    statement-level or row-level <command>UPDATE</command>,
+    <command>DELETE</command> and <command>INSERT</command> triggers are fired
+    depending on what actions are specified in the <command>MERGE</command> query
+    and what actions are activated.
+   </para>
+
+   <para>
+    While running a <command>MERGE</command> command, statement-level
+    <literal>BEFORE</literal> and <literal>AFTER</literal> triggers are fired for
+    events specified in the actions of the <command>MERGE</command> command,
+    irrespective of whether the action is finally activated or not. This is same as
+    an <command>UPDATE</command> statement that updates no rows, yet
+    statement-level triggers are fired. The row-level triggers are fired only
+    when a row is actually updated, inserted or deleted. So it's perfectly legal
+    that while statement-level triggers are fired for certain type of action, no
+    row-level triggers are fired for the same kind of action.
+   </para>
+
    <para>
     Trigger functions invoked by per-statement triggers should always
     return <symbol>NULL</symbol>. Trigger functions invoked by per-row
diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
index 9650145642..867a217626 100644
--- a/src/backend/access/heap/heapam.c
+++ b/src/backend/access/heap/heapam.c
@@ -3235,6 +3235,7 @@ l1:
 			   result == HeapTupleUpdated ||
 			   result == HeapTupleBeingUpdated);
 		Assert(!(tp.t_data->t_infomask & HEAP_XMAX_INVALID));
+		hufd->result = result;
 		hufd->ctid = tp.t_data->t_ctid;
 		hufd->xmax = HeapTupleHeaderGetUpdateXid(tp.t_data);
 		if (result == HeapTupleSelfUpdated)
@@ -3505,7 +3506,7 @@ simple_heap_delete(Relation relation, ItemPointer tid)
 HTSU_Result
 heap_update(Relation relation, ItemPointer otid, HeapTuple newtup,
 			CommandId cid, Snapshot crosscheck, bool wait,
-			HeapUpdateFailureData *hufd, LockTupleMode *lockmode)
+			HeapUpdateFailureData *hufd)
 {
 	HTSU_Result result;
 	TransactionId xid = GetCurrentTransactionId();
@@ -3545,8 +3546,10 @@ heap_update(Relation relation, ItemPointer otid, HeapTuple newtup,
 				infomask2_old_tuple,
 				infomask_new_tuple,
 				infomask2_new_tuple;
+	LockTupleMode	lockmode;
 
 	Assert(ItemPointerIsValid(otid));
+	Assert(hufd != NULL);
 
 	/*
 	 * Forbid this during a parallel operation, lest it allocate a combocid.
@@ -3647,7 +3650,7 @@ heap_update(Relation relation, ItemPointer otid, HeapTuple newtup,
 	 */
 	if (!bms_overlap(modified_attrs, key_attrs))
 	{
-		*lockmode = LockTupleNoKeyExclusive;
+		lockmode = hufd->lockmode = LockTupleNoKeyExclusive;
 		mxact_status = MultiXactStatusNoKeyUpdate;
 		key_intact = true;
 
@@ -3664,7 +3667,7 @@ heap_update(Relation relation, ItemPointer otid, HeapTuple newtup,
 	}
 	else
 	{
-		*lockmode = LockTupleExclusive;
+		lockmode = hufd->lockmode = LockTupleExclusive;
 		mxact_status = MultiXactStatusUpdate;
 		key_intact = false;
 	}
@@ -3742,12 +3745,12 @@ l2:
 			int			remain;
 
 			if (DoesMultiXactIdConflict((MultiXactId) xwait, infomask,
-										*lockmode))
+										lockmode))
 			{
 				LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
 
 				/* acquire tuple lock, if necessary */
-				heap_acquire_tuplock(relation, &(oldtup.t_self), *lockmode,
+				heap_acquire_tuplock(relation, &(oldtup.t_self), lockmode,
 									 LockWaitBlock, &have_tuple_lock);
 
 				/* wait for multixact */
@@ -3831,7 +3834,7 @@ l2:
 			 * lock.
 			 */
 			LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
-			heap_acquire_tuplock(relation, &(oldtup.t_self), *lockmode,
+			heap_acquire_tuplock(relation, &(oldtup.t_self), lockmode,
 								 LockWaitBlock, &have_tuple_lock);
 			XactLockTableWait(xwait, relation, &oldtup.t_self,
 							  XLTW_Update);
@@ -3870,6 +3873,7 @@ l2:
 			   result == HeapTupleUpdated ||
 			   result == HeapTupleBeingUpdated);
 		Assert(!(oldtup.t_data->t_infomask & HEAP_XMAX_INVALID));
+		hufd->result = result;
 		hufd->ctid = oldtup.t_data->t_ctid;
 		hufd->xmax = HeapTupleHeaderGetUpdateXid(oldtup.t_data);
 		if (result == HeapTupleSelfUpdated)
@@ -3878,7 +3882,7 @@ l2:
 			hufd->cmax = InvalidCommandId;
 		UnlockReleaseBuffer(buffer);
 		if (have_tuple_lock)
-			UnlockTupleTuplock(relation, &(oldtup.t_self), *lockmode);
+			UnlockTupleTuplock(relation, &(oldtup.t_self), lockmode);
 		if (vmbuffer != InvalidBuffer)
 			ReleaseBuffer(vmbuffer);
 		bms_free(hot_attrs);
@@ -3916,7 +3920,7 @@ l2:
 	compute_new_xmax_infomask(HeapTupleHeaderGetRawXmax(oldtup.t_data),
 							  oldtup.t_data->t_infomask,
 							  oldtup.t_data->t_infomask2,
-							  xid, *lockmode, true,
+							  xid, lockmode, true,
 							  &xmax_old_tuple, &infomask_old_tuple,
 							  &infomask2_old_tuple);
 
@@ -4033,7 +4037,7 @@ l2:
 		compute_new_xmax_infomask(HeapTupleHeaderGetRawXmax(oldtup.t_data),
 								  oldtup.t_data->t_infomask,
 								  oldtup.t_data->t_infomask2,
-								  xid, *lockmode, false,
+								  xid, lockmode, false,
 								  &xmax_lock_old_tuple, &infomask_lock_old_tuple,
 								  &infomask2_lock_old_tuple);
 
@@ -4345,7 +4349,7 @@ l2:
 	 * Release the lmgr tuple lock, if we had it.
 	 */
 	if (have_tuple_lock)
-		UnlockTupleTuplock(relation, &(oldtup.t_self), *lockmode);
+		UnlockTupleTuplock(relation, &(oldtup.t_self), lockmode);
 
 	pgstat_count_heap_update(relation, use_hot_update);
 
@@ -4572,12 +4576,11 @@ simple_heap_update(Relation relation, ItemPointer otid, HeapTuple tup)
 {
 	HTSU_Result result;
 	HeapUpdateFailureData hufd;
-	LockTupleMode lockmode;
 
 	result = heap_update(relation, otid, tup,
 						 GetCurrentCommandId(true), InvalidSnapshot,
 						 true /* wait for commit */ ,
-						 &hufd, &lockmode);
+						 &hufd);
 	switch (result)
 	{
 		case HeapTupleSelfUpdated:
@@ -5163,6 +5166,7 @@ failed:
 		Assert(result == HeapTupleSelfUpdated || result == HeapTupleUpdated ||
 			   result == HeapTupleWouldBlock);
 		Assert(!(tuple->t_data->t_infomask & HEAP_XMAX_INVALID));
+		hufd->result = result;
 		hufd->ctid = tuple->t_data->t_ctid;
 		hufd->xmax = HeapTupleHeaderGetUpdateXid(tuple->t_data);
 		if (result == HeapTupleSelfUpdated)
diff --git a/src/backend/catalog/sql_features.txt b/src/backend/catalog/sql_features.txt
index aeb262a5b0..2a094c19ac 100644
--- a/src/backend/catalog/sql_features.txt
+++ b/src/backend/catalog/sql_features.txt
@@ -229,9 +229,9 @@ F311	Schema definition statement	02	CREATE TABLE for persistent base tables	YES
 F311	Schema definition statement	03	CREATE VIEW	YES	
 F311	Schema definition statement	04	CREATE VIEW: WITH CHECK OPTION	YES	
 F311	Schema definition statement	05	GRANT statement	YES	
-F312	MERGE statement			NO	consider INSERT ... ON CONFLICT DO UPDATE
-F313	Enhanced MERGE statement			NO	
-F314	MERGE statement with DELETE branch			NO	
+F312	MERGE statement			YES	also consider INSERT ... ON CONFLICT DO UPDATE
+F313	Enhanced MERGE statement			YES	
+F314	MERGE statement with DELETE branch			YES	
 F321	User authorization			YES	
 F341	Usage tables			NO	no ROUTINE_*_USAGE tables
 F361	Subprogram support			YES	
diff --git a/src/backend/commands/explain.c b/src/backend/commands/explain.c
index de09ded65b..0efc1cf96f 100644
--- a/src/backend/commands/explain.c
+++ b/src/backend/commands/explain.c
@@ -1023,6 +1023,9 @@ ExplainNode(PlanState *planstate, List *ancestors,
 				case CMD_DELETE:
 					pname = operation = "Delete";
 					break;
+				case CMD_MERGE:
+					pname = operation = "Merge";
+					break;
 				default:
 					pname = "???";
 					break;
@@ -1534,7 +1537,7 @@ ExplainNode(PlanState *planstate, List *ancestors,
 										   planstate, es);
 			if (es->analyze)
 				ExplainPropertyFloat("Heap Fetches", NULL,
-									 planstate->instrument->ntuples2, 0, es);
+									 planstate->instrument->node_ntuples1, 0, es);
 			break;
 		case T_BitmapIndexScan:
 			show_scan_qual(((BitmapIndexScan *) plan)->indexqualorig,
@@ -3105,6 +3108,10 @@ show_modifytable_info(ModifyTableState *mtstate, List *ancestors,
 			operation = "Delete";
 			foperation = "Foreign Delete";
 			break;
+		case CMD_MERGE:
+			operation = "Merge";
+			foperation = "Foreign Merge";
+			break;
 		default:
 			operation = "???";
 			foperation = "Foreign ???";
@@ -3218,7 +3225,7 @@ show_modifytable_info(ModifyTableState *mtstate, List *ancestors,
 
 			/* count the number of source rows */
 			total = mtstate->mt_plans[0]->instrument->ntuples;
-			other_path = mtstate->ps.instrument->ntuples2;
+			other_path = mtstate->ps.instrument->node_ntuples1;
 			insert_path = total - other_path;
 
 			ExplainPropertyFloat("Tuples Inserted", NULL,
@@ -3227,6 +3234,32 @@ show_modifytable_info(ModifyTableState *mtstate, List *ancestors,
 								 other_path, 0, es);
 		}
 	}
+	else if (node->operation == CMD_MERGE)
+	{
+		/* EXPLAIN ANALYZE display of actual outcome for each tuple proposed */
+		if (es->analyze && mtstate->ps.instrument)
+		{
+			double		total;
+			double		insert_path;
+			double		update_path;
+			double		delete_path;
+			double		skipped_path;
+
+			InstrEndLoop(mtstate->mt_plans[0]->instrument);
+
+			/* count the number of source rows */
+			total = mtstate->mt_plans[0]->instrument->ntuples;
+			insert_path = mtstate->ps.instrument->node_ntuples1;
+			update_path = mtstate->ps.instrument->node_ntuples2;
+			delete_path = mtstate->ps.instrument->node_ntuples3;
+			skipped_path = total - insert_path - update_path - delete_path;
+
+			ExplainPropertyFloat("Tuples Inserted", NULL, insert_path, 0, es);
+			ExplainPropertyFloat("Tuples Updated", NULL, update_path, 0, es);
+			ExplainPropertyFloat("Tuples Deleted", NULL, delete_path, 0, es);
+			ExplainPropertyFloat("Tuples Skipped", NULL, skipped_path, 0, es);
+		}
+	}
 
 	if (labeltargets)
 		ExplainCloseGroup("Target Tables", "Target Tables", false, es);
diff --git a/src/backend/commands/prepare.c b/src/backend/commands/prepare.c
index 6036b735e9..f8ee6eb7bd 100644
--- a/src/backend/commands/prepare.c
+++ b/src/backend/commands/prepare.c
@@ -151,6 +151,7 @@ PrepareQuery(PrepareStmt *stmt, const char *queryString,
 		case CMD_INSERT:
 		case CMD_UPDATE:
 		case CMD_DELETE:
+		case CMD_MERGE:
 			/* OK */
 			break;
 		default:
diff --git a/src/backend/commands/trigger.c b/src/backend/commands/trigger.c
index bcdd86ce92..4c33a53b1a 100644
--- a/src/backend/commands/trigger.c
+++ b/src/backend/commands/trigger.c
@@ -85,7 +85,8 @@ static HeapTuple GetTupleForTrigger(EState *estate,
 				   ResultRelInfo *relinfo,
 				   ItemPointer tid,
 				   LockTupleMode lockmode,
-				   TupleTableSlot **newSlot);
+				   TupleTableSlot **newSlot,
+				   HeapUpdateFailureData *hufdp);
 static bool TriggerEnabled(EState *estate, ResultRelInfo *relinfo,
 			   Trigger *trigger, TriggerEvent event,
 			   Bitmapset *modifiedCols,
@@ -95,6 +96,12 @@ static HeapTuple ExecCallTriggerFunc(TriggerData *trigdata,
 					FmgrInfo *finfo,
 					Instrumentation *instr,
 					MemoryContext per_tuple_context);
+static Tuplestorestate *AfterTriggerGetTransitionTable(int event,
+					HeapTuple oldtup,
+					HeapTuple newtup,
+					TransitionCaptureState *transition_capture);
+static void TransitionTableAddTuple(HeapTuple heaptup, Tuplestorestate *tuplestore,
+					TupleConversionMap *map);
 static void AfterTriggerSaveEvent(EState *estate, ResultRelInfo *relinfo,
 					  int event, bool row_trigger,
 					  HeapTuple oldtup, HeapTuple newtup,
@@ -2756,7 +2763,8 @@ ExecBRDeleteTriggers(EState *estate, EPQState *epqstate,
 					 ResultRelInfo *relinfo,
 					 ItemPointer tupleid,
 					 HeapTuple fdw_trigtuple,
-					 TupleTableSlot **epqslot)
+					 TupleTableSlot **epqslot,
+					 HeapUpdateFailureData *hufdp)
 {
 	TriggerDesc *trigdesc = relinfo->ri_TrigDesc;
 	bool		result = true;
@@ -2770,7 +2778,7 @@ ExecBRDeleteTriggers(EState *estate, EPQState *epqstate,
 	if (fdw_trigtuple == NULL)
 	{
 		trigtuple = GetTupleForTrigger(estate, epqstate, relinfo, tupleid,
-									   LockTupleExclusive, &newSlot);
+									   LockTupleExclusive, &newSlot, hufdp);
 		if (trigtuple == NULL)
 			return false;
 
@@ -2853,6 +2861,7 @@ ExecARDeleteTriggers(EState *estate, ResultRelInfo *relinfo,
 										   relinfo,
 										   tupleid,
 										   LockTupleExclusive,
+										   NULL,
 										   NULL);
 		else
 			trigtuple = fdw_trigtuple;
@@ -2990,7 +2999,8 @@ ExecBRUpdateTriggers(EState *estate, EPQState *epqstate,
 					 ResultRelInfo *relinfo,
 					 ItemPointer tupleid,
 					 HeapTuple fdw_trigtuple,
-					 TupleTableSlot *slot)
+					 TupleTableSlot *slot,
+					 HeapUpdateFailureData *hufdp)
 {
 	TriggerDesc *trigdesc = relinfo->ri_TrigDesc;
 	HeapTuple	slottuple = ExecFetchSlotHeapTuple(slot, true, NULL);
@@ -3011,7 +3021,7 @@ ExecBRUpdateTriggers(EState *estate, EPQState *epqstate,
 	{
 		/* get a copy of the on-disk tuple we are planning to update */
 		trigtuple = GetTupleForTrigger(estate, epqstate, relinfo, tupleid,
-									   lockmode, &newSlot);
+									   lockmode, &newSlot, hufdp);
 		if (trigtuple == NULL)
 			return NULL;		/* cancel the update action */
 	}
@@ -3131,6 +3141,7 @@ ExecARUpdateTriggers(EState *estate, ResultRelInfo *relinfo,
 										   relinfo,
 										   tupleid,
 										   LockTupleExclusive,
+										   NULL,
 										   NULL);
 		else
 			trigtuple = fdw_trigtuple;
@@ -3279,7 +3290,8 @@ GetTupleForTrigger(EState *estate,
 				   ResultRelInfo *relinfo,
 				   ItemPointer tid,
 				   LockTupleMode lockmode,
-				   TupleTableSlot **newSlot)
+				   TupleTableSlot **newSlot,
+				   HeapUpdateFailureData *hufdp)
 {
 	Relation	relation = relinfo->ri_RelationDesc;
 	HeapTupleData tuple;
@@ -3305,6 +3317,11 @@ ltrmark:;
 							   estate->es_output_cid,
 							   lockmode, LockWaitBlock,
 							   false, &buffer, &hufd);
+
+		/* Let the caller know about failure reason, if any. */
+		if (hufdp)
+			*hufdp = hufd;
+
 		switch (test)
 		{
 			case HeapTupleSelfUpdated:
@@ -3346,10 +3363,17 @@ ltrmark:;
 					/* it was updated, so look at the updated version */
 					TupleTableSlot *epqslot;
 
+					/*
+					 * If we're running MERGE then we must install the
+					 * new tuple in the slot of the underlying join query and
+					 * not the result relation itself. If the join does not
+					 * yield any tuple, the caller will take the necessary
+					 * action.
+					 */
 					epqslot = EvalPlanQual(estate,
 										   epqstate,
 										   relation,
-										   relinfo->ri_RangeTableIndex,
+										   GetEPQRangeTableIndex(relinfo),
 										   lockmode,
 										   &hufd.ctid,
 										   hufd.xmax);
@@ -3876,8 +3900,22 @@ struct AfterTriggersTableData
 	bool		before_trig_done;	/* did we already queue BS triggers? */
 	bool		after_trig_done;	/* did we already queue AS triggers? */
 	AfterTriggerEventList after_trig_events;	/* if so, saved list pointer */
-	Tuplestorestate *old_tuplestore;	/* "old" transition table, if any */
-	Tuplestorestate *new_tuplestore;	/* "new" transition table, if any */
+
+	/*
+	 * We maintain separate transaction tables for UPDATE/INSERT/DELETE since
+	 * MERGE can run all three actions in a single statement. Note that UPDATE
+	 * needs both old and new transition tables whereas INSERT needs only new
+	 * and DELETE needs only old.
+	 */
+
+	/* "old" transition table for UPDATE, if any */
+	Tuplestorestate *old_upd_tuplestore;
+	/* "new" transition table for UPDATE, if any */
+	Tuplestorestate *new_upd_tuplestore;
+	/* "old" transition table for DELETE, if any */
+	Tuplestorestate *old_del_tuplestore;
+	/* "new" transition table INSERT, if any */
+	Tuplestorestate *new_ins_tuplestore;
 };
 
 static AfterTriggersData afterTriggers;
@@ -4344,13 +4382,19 @@ AfterTriggerExecute(AfterTriggerEvent event,
 	{
 		if (LocTriggerData.tg_trigger->tgoldtable)
 		{
-			LocTriggerData.tg_oldtable = evtshared->ats_table->old_tuplestore;
+			if (TRIGGER_FIRED_BY_UPDATE(evtshared->ats_event))
+				LocTriggerData.tg_oldtable = evtshared->ats_table->old_upd_tuplestore;
+			else
+				LocTriggerData.tg_oldtable = evtshared->ats_table->old_del_tuplestore;
 			evtshared->ats_table->closed = true;
 		}
 
 		if (LocTriggerData.tg_trigger->tgnewtable)
 		{
-			LocTriggerData.tg_newtable = evtshared->ats_table->new_tuplestore;
+			if (TRIGGER_FIRED_BY_INSERT(evtshared->ats_event))
+				LocTriggerData.tg_newtable = evtshared->ats_table->new_ins_tuplestore;
+			else
+				LocTriggerData.tg_newtable = evtshared->ats_table->new_upd_tuplestore;
 			evtshared->ats_table->closed = true;
 		}
 	}
@@ -4687,8 +4731,10 @@ TransitionCaptureState *
 MakeTransitionCaptureState(TriggerDesc *trigdesc, Oid relid, CmdType cmdType)
 {
 	TransitionCaptureState *state;
-	bool		need_old,
-				need_new;
+	bool		need_old_upd,
+				need_new_upd,
+				need_old_del,
+				need_new_ins;
 	AfterTriggersTableData *table;
 	MemoryContext oldcxt;
 	ResourceOwner saveResourceOwner;
@@ -4700,23 +4746,31 @@ MakeTransitionCaptureState(TriggerDesc *trigdesc, Oid relid, CmdType cmdType)
 	switch (cmdType)
 	{
 		case CMD_INSERT:
-			need_old = false;
-			need_new = trigdesc->trig_insert_new_table;
+			need_old_upd = need_old_del = need_new_upd = false;
+			need_new_ins = trigdesc->trig_insert_new_table;
 			break;
 		case CMD_UPDATE:
-			need_old = trigdesc->trig_update_old_table;
-			need_new = trigdesc->trig_update_new_table;
+			need_old_upd = trigdesc->trig_update_old_table;
+			need_new_upd = trigdesc->trig_update_new_table;
+			need_old_del = need_new_ins = false;
 			break;
 		case CMD_DELETE:
-			need_old = trigdesc->trig_delete_old_table;
-			need_new = false;
+			need_old_del = trigdesc->trig_delete_old_table;
+			need_old_upd = need_new_upd = need_new_ins = false;
+			break;
+		case CMD_MERGE:
+			need_old_upd = trigdesc->trig_update_old_table;
+			need_new_upd = trigdesc->trig_update_new_table;
+			need_old_del = trigdesc->trig_delete_old_table;
+			need_new_ins = trigdesc->trig_insert_new_table;
 			break;
 		default:
 			elog(ERROR, "unexpected CmdType: %d", (int) cmdType);
-			need_old = need_new = false;	/* keep compiler quiet */
+			/* keep compiler quiet */
+			need_old_upd = need_new_upd = need_old_del = need_new_ins = false;
 			break;
 	}
-	if (!need_old && !need_new)
+	if (!need_old_upd && !need_new_upd && !need_new_ins && !need_old_del)
 		return NULL;
 
 	/* Check state, like AfterTriggerSaveEvent. */
@@ -4746,10 +4800,14 @@ MakeTransitionCaptureState(TriggerDesc *trigdesc, Oid relid, CmdType cmdType)
 	saveResourceOwner = CurrentResourceOwner;
 	CurrentResourceOwner = CurTransactionResourceOwner;
 
-	if (need_old && table->old_tuplestore == NULL)
-		table->old_tuplestore = tuplestore_begin_heap(false, false, work_mem);
-	if (need_new && table->new_tuplestore == NULL)
-		table->new_tuplestore = tuplestore_begin_heap(false, false, work_mem);
+	if (need_old_upd && table->old_upd_tuplestore == NULL)
+		table->old_upd_tuplestore = tuplestore_begin_heap(false, false, work_mem);
+	if (need_new_upd && table->new_upd_tuplestore == NULL)
+		table->new_upd_tuplestore = tuplestore_begin_heap(false, false, work_mem);
+	if (need_old_del && table->old_del_tuplestore == NULL)
+		table->old_del_tuplestore = tuplestore_begin_heap(false, false, work_mem);
+	if (need_new_ins && table->new_ins_tuplestore == NULL)
+		table->new_ins_tuplestore = tuplestore_begin_heap(false, false, work_mem);
 
 	CurrentResourceOwner = saveResourceOwner;
 	MemoryContextSwitchTo(oldcxt);
@@ -4938,12 +4996,20 @@ AfterTriggerFreeQuery(AfterTriggersQueryData *qs)
 	{
 		AfterTriggersTableData *table = (AfterTriggersTableData *) lfirst(lc);
 
-		ts = table->old_tuplestore;
-		table->old_tuplestore = NULL;
+		ts = table->old_upd_tuplestore;
+		table->old_upd_tuplestore = NULL;
+		if (ts)
+			tuplestore_end(ts);
+		ts = table->new_upd_tuplestore;
+		table->new_upd_tuplestore = NULL;
+		if (ts)
+			tuplestore_end(ts);
+		ts = table->old_del_tuplestore;
+		table->old_del_tuplestore = NULL;
 		if (ts)
 			tuplestore_end(ts);
-		ts = table->new_tuplestore;
-		table->new_tuplestore = NULL;
+		ts = table->new_ins_tuplestore;
+		table->new_ins_tuplestore = NULL;
 		if (ts)
 			tuplestore_end(ts);
 	}
@@ -5716,6 +5782,84 @@ AfterTriggerPendingOnRel(Oid relid)
 	return false;
 }
 
+/*
+ * Get the transition table for the given event and depending on whether we are
+ * processing the old or the new tuple.
+ */
+static Tuplestorestate *
+AfterTriggerGetTransitionTable(int event,
+							   HeapTuple oldtup,
+							   HeapTuple newtup,
+							   TransitionCaptureState *transition_capture)
+{
+	Tuplestorestate	*tuplestore = NULL;
+	bool			delete_old_table = transition_capture->tcs_delete_old_table;
+	bool			update_old_table = transition_capture->tcs_update_old_table;
+	bool			update_new_table = transition_capture->tcs_update_new_table;
+	bool			insert_new_table = transition_capture->tcs_insert_new_table;;
+
+	/*
+	 * For INSERT events newtup should be non-NULL, for DELETE events
+	 * oldtup should be non-NULL, whereas for UPDATE events normally both
+	 * oldtup and newtup are non-NULL.  But for UPDATE events fired for
+	 * capturing transition tuples during UPDATE partition-key row
+	 * movement, oldtup is NULL when the event is for a row being inserted,
+	 * whereas newtup is NULL when the event is for a row being deleted.
+	 */
+	Assert(!(event == TRIGGER_EVENT_DELETE && delete_old_table &&
+				oldtup == NULL));
+	Assert(!(event == TRIGGER_EVENT_INSERT && insert_new_table &&
+				newtup == NULL));
+
+	/*
+	 * We're called either for the newtup or the oldtup, but not both at the
+	 * same time.
+	 */
+	Assert((oldtup != NULL) ^ (newtup != NULL));
+
+	if (oldtup != NULL)
+	{
+		if (event == TRIGGER_EVENT_DELETE && delete_old_table)
+			tuplestore = transition_capture->tcs_private->old_del_tuplestore;
+		else if (event == TRIGGER_EVENT_UPDATE && update_old_table)
+			tuplestore = transition_capture->tcs_private->old_upd_tuplestore;
+	}
+
+	if (newtup != NULL)
+	{
+		if (event == TRIGGER_EVENT_INSERT && insert_new_table)
+			tuplestore = transition_capture->tcs_private->new_ins_tuplestore;
+		else if (event == TRIGGER_EVENT_UPDATE && update_new_table)
+			tuplestore = transition_capture->tcs_private->new_upd_tuplestore;
+	}
+
+	return tuplestore;
+}
+
+/*
+ * Add the given heap tuple to the given tuplestore, applying the conversion
+ * map if necessary.
+ */
+static void
+TransitionTableAddTuple(HeapTuple heaptup, Tuplestorestate *tuplestore,
+						TupleConversionMap *map)
+{
+	/*
+	 * Nothing needs to be done if we don't have a tuplestore.
+	 */
+	if (tuplestore == NULL)
+		return;
+
+	if (map != NULL)
+	{
+		HeapTuple	converted = execute_attr_map_tuple(heaptup, map);
+
+		tuplestore_puttuple(tuplestore, converted);
+		pfree(converted);
+	}
+	else
+		tuplestore_puttuple(tuplestore, heaptup);
+}
 
 /* ----------
  * AfterTriggerSaveEvent()
@@ -5777,10 +5921,6 @@ AfterTriggerSaveEvent(EState *estate, ResultRelInfo *relinfo,
 	{
 		HeapTuple	original_insert_tuple = transition_capture->tcs_original_insert_tuple;
 		TupleConversionMap *map = transition_capture->tcs_map;
-		bool		delete_old_table = transition_capture->tcs_delete_old_table;
-		bool		update_old_table = transition_capture->tcs_update_old_table;
-		bool		update_new_table = transition_capture->tcs_update_new_table;
-		bool		insert_new_table = transition_capture->tcs_insert_new_table;;
 
 		/*
 		 * For INSERT events newtup should be non-NULL, for DELETE events
@@ -5791,48 +5931,32 @@ AfterTriggerSaveEvent(EState *estate, ResultRelInfo *relinfo,
 		 * inserted, whereas newtup is NULL when the event is for a row being
 		 * deleted.
 		 */
-		Assert(!(event == TRIGGER_EVENT_DELETE && delete_old_table &&
-				 oldtup == NULL));
-		Assert(!(event == TRIGGER_EVENT_INSERT && insert_new_table &&
-				 newtup == NULL));
-
-		if (oldtup != NULL &&
-			((event == TRIGGER_EVENT_DELETE && delete_old_table) ||
-			 (event == TRIGGER_EVENT_UPDATE && update_old_table)))
+		if (oldtup != NULL)
 		{
-			Tuplestorestate *old_tuplestore;
-
-			old_tuplestore = transition_capture->tcs_private->old_tuplestore;
-
-			if (map != NULL)
-			{
-				HeapTuple	converted = execute_attr_map_tuple(oldtup, map);
-
-				tuplestore_puttuple(old_tuplestore, converted);
-				pfree(converted);
-			}
-			else
-				tuplestore_puttuple(old_tuplestore, oldtup);
+			Tuplestorestate *tuplestore =
+				AfterTriggerGetTransitionTable(event,
+											   oldtup,
+											   NULL,
+											   transition_capture);
+			TransitionTableAddTuple(oldtup, tuplestore, map);
 		}
-		if (newtup != NULL &&
-			((event == TRIGGER_EVENT_INSERT && insert_new_table) ||
-			 (event == TRIGGER_EVENT_UPDATE && update_new_table)))
-		{
-			Tuplestorestate *new_tuplestore;
 
-			new_tuplestore = transition_capture->tcs_private->new_tuplestore;
+		/*
+		 * Capture the new tuple in the appropriate transition table based on
+		 * the event.
+		 */
+		if (newtup != NULL)
+		{
+			Tuplestorestate *tuplestore =
+				AfterTriggerGetTransitionTable(event,
+											   NULL,
+											   newtup,
+											   transition_capture);
 
 			if (original_insert_tuple != NULL)
-				tuplestore_puttuple(new_tuplestore, original_insert_tuple);
-			else if (map != NULL)
-			{
-				HeapTuple	converted = execute_attr_map_tuple(newtup, map);
-
-				tuplestore_puttuple(new_tuplestore, converted);
-				pfree(converted);
-			}
+				tuplestore_puttuple(tuplestore, original_insert_tuple);
 			else
-				tuplestore_puttuple(new_tuplestore, newtup);
+				TransitionTableAddTuple(newtup, tuplestore, map);
 		}
 
 		/*
diff --git a/src/backend/executor/Makefile b/src/backend/executor/Makefile
index cc09895fa5..76d87eea49 100644
--- a/src/backend/executor/Makefile
+++ b/src/backend/executor/Makefile
@@ -14,7 +14,7 @@ include $(top_builddir)/src/Makefile.global
 
 OBJS = execAmi.o execCurrent.o execExpr.o execExprInterp.o \
        execGrouping.o execIndexing.o execJunk.o \
-       execMain.o execParallel.o execPartition.o execProcnode.o \
+       execMain.o execMerge.o execParallel.o execPartition.o execProcnode.o \
        execReplication.o execScan.o execSRF.o execTuples.o \
        execUtils.o functions.o instrument.o nodeAppend.o nodeAgg.o \
        nodeBitmapAnd.o nodeBitmapOr.o \
diff --git a/src/backend/executor/README b/src/backend/executor/README
index ddbd62b4db..c325a50b08 100644
--- a/src/backend/executor/README
+++ b/src/backend/executor/README
@@ -37,6 +37,17 @@ the plan tree returns the computed tuples to be updated, plus a "junk"
 one.  For DELETE, the plan tree need only deliver a CTID column, and the
 ModifyTable node visits each of those rows and marks the row deleted.
 
+MERGE runs one generic plan that returns candidate target rows. Each row
+consists of a super-row that contains all the columns needed by any of the
+individual actions, plus CTID and TABLEOID junk columns. The CTID column is
+required to know if a matching target row was found or not and the TABLEOID
+column is needed to find the underlying target partition, in case when the
+target table is a partitioned table. When a matching target tuple is found,
+the CTID column identifies the matching tuple and we attempt to activate
+WHEN MATCHED actions. If a matching tuple is not found, then CTID column is
+NULL and we attempt to activate WHEN NOT MATCHED actions. Once we know which
+action is activated we form the final result row and apply only those changes.
+
 XXX a great deal more documentation needs to be written here...
 
 
diff --git a/src/backend/executor/execMain.c b/src/backend/executor/execMain.c
index d83d296d82..3bfd4083a2 100644
--- a/src/backend/executor/execMain.c
+++ b/src/backend/executor/execMain.c
@@ -234,6 +234,7 @@ standard_ExecutorStart(QueryDesc *queryDesc, int eflags)
 		case CMD_INSERT:
 		case CMD_DELETE:
 		case CMD_UPDATE:
+		case CMD_MERGE:
 			estate->es_output_cid = GetCurrentCommandId(true);
 			break;
 
@@ -1326,6 +1327,9 @@ InitResultRelInfo(ResultRelInfo *resultRelInfo,
 	resultRelInfo->ri_onConflictArbiterIndexes = NIL;
 	resultRelInfo->ri_onConflict = NULL;
 
+	resultRelInfo->ri_mergeTargetRTI = 0;
+	resultRelInfo->ri_mergeState = (MergeState *) palloc0(sizeof (MergeState));
+
 	/*
 	 * Partition constraint, which also includes the partition constraint of
 	 * all the ancestors that are partitions.  Note that it will be checked
@@ -2137,6 +2141,19 @@ ExecWithCheckOptions(WCOKind kind, ResultRelInfo *resultRelInfo,
 								 errmsg("new row violates row-level security policy for table \"%s\"",
 										wco->relname)));
 					break;
+				case WCO_RLS_MERGE_UPDATE_CHECK:
+				case WCO_RLS_MERGE_DELETE_CHECK:
+					if (wco->polname != NULL)
+						ereport(ERROR,
+								(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
+								 errmsg("target row violates row-level security policy \"%s\" (USING expression) for table \"%s\"",
+										wco->polname, wco->relname)));
+					else
+						ereport(ERROR,
+								(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
+								 errmsg("target row violates row-level security policy (USING expression) for table \"%s\"",
+										wco->relname)));
+					break;
 				case WCO_RLS_CONFLICT_CHECK:
 					if (wco->polname != NULL)
 						ereport(ERROR,
diff --git a/src/backend/executor/execMerge.c b/src/backend/executor/execMerge.c
new file mode 100644
index 0000000000..4d252d2ee5
--- /dev/null
+++ b/src/backend/executor/execMerge.c
@@ -0,0 +1,679 @@
+/*-------------------------------------------------------------------------
+ *
+ * execMerge.c
+ *	  routines to handle Merge nodes relating to the MERGE command
+ *
+ * Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/executor/execMerge.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+
+#include "postgres.h"
+
+#include "access/htup_details.h"
+#include "access/xact.h"
+#include "commands/trigger.h"
+#include "executor/execPartition.h"
+#include "executor/executor.h"
+#include "executor/nodeModifyTable.h"
+#include "executor/execMerge.h"
+#include "miscadmin.h"
+#include "nodes/nodeFuncs.h"
+#include "storage/bufmgr.h"
+#include "storage/lmgr.h"
+#include "utils/builtins.h"
+#include "utils/memutils.h"
+#include "utils/rel.h"
+#include "utils/tqual.h"
+
+static void ExecMergeNotMatched(ModifyTableState *mtstate, EState *estate,
+								TupleTableSlot *slot);
+static bool ExecMergeMatched(ModifyTableState *mtstate, EState *estate,
+							 TupleTableSlot *slot, JunkFilter *junkfilter,
+							 ItemPointer tupleid);
+/*
+ * Perform MERGE.
+ */
+void
+ExecMerge(ModifyTableState *mtstate, EState *estate, TupleTableSlot *slot,
+		  JunkFilter *junkfilter, ResultRelInfo *resultRelInfo)
+{
+	ExprContext *econtext = mtstate->ps.ps_ExprContext;
+	ItemPointer tupleid;
+	ItemPointerData tuple_ctid;
+	bool		matched = false;
+	Datum		datum;
+	bool		isNull;
+
+	Assert(resultRelInfo->ri_RelationDesc->rd_rel->relkind == RELKIND_RELATION ||
+		   resultRelInfo->ri_RelationDesc->rd_rel->relkind == RELKIND_PARTITIONED_TABLE);
+
+	/*
+	 * Reset per-tuple memory context to free any expression evaluation
+	 * storage allocated in the previous cycle.
+	 */
+	ResetExprContext(econtext);
+
+	/*
+	 * We run a JOIN between the target relation and the source relation to
+	 * find a set of candidate source rows that has matching row in the target
+	 * table and a set of candidate source rows that does not have matching
+	 * row in the target table. If the join returns us a tuple with target
+	 * relation's tid set, that implies that the join found a matching row for
+	 * the given source tuple. This case triggers the WHEN MATCHED clause of
+	 * the MERGE. Whereas a NULL in the target relation's ctid column
+	 * indicates a NOT MATCHED case.
+	 */
+	datum = ExecGetJunkAttribute(slot, junkfilter->jf_junkAttNo, &isNull);
+
+	if (!isNull)
+	{
+		matched = true;
+		tupleid = (ItemPointer) DatumGetPointer(datum);
+		tuple_ctid = *tupleid;	/* be sure we don't free ctid!! */
+		tupleid = &tuple_ctid;
+	}
+	else
+	{
+		matched = false;
+		tupleid = NULL;			/* we don't need it for INSERT actions */
+	}
+
+	/*
+	 * If we are dealing with a WHEN MATCHED case, we execute the first action
+	 * for which the additional WHEN MATCHED AND quals pass. If an action
+	 * without quals is found, that action is executed.
+	 *
+	 * Similarly, if we are dealing with WHEN NOT MATCHED case, we look at the
+	 * given WHEN NOT MATCHED actions in sequence until one passes.
+	 *
+	 * Things get interesting in case of concurrent update/delete of the
+	 * target tuple. Such concurrent update/delete is detected while we are
+	 * executing a WHEN MATCHED action.
+	 *
+	 * A concurrent update can:
+	 *
+	 * 1. modify the target tuple so that it no longer satisfies the
+	 * additional quals attached to the current WHEN MATCHED action OR
+	 *
+	 * In this case, we are still dealing with a WHEN MATCHED case, but
+	 * we should recheck the list of WHEN MATCHED actions and choose the first
+	 * one that satisfies the new target tuple.
+	 *
+	 * 2. modify the target tuple so that the join quals no longer pass and
+	 * hence the source tuple no longer has a match.
+	 *
+	 * In the second case, the source tuple no longer matches the target tuple,
+	 * so we now instead find a qualifying WHEN NOT MATCHED action to execute.
+	 *
+	 * A concurrent delete, changes a WHEN MATCHED case to WHEN NOT MATCHED.
+	 *
+	 * ExecMergeMatched takes care of following the update chain and
+	 * re-finding the qualifying WHEN MATCHED action, as long as the updated
+	 * target tuple still satisfies the join quals i.e. it still remains a
+	 * WHEN MATCHED case. If the tuple gets deleted or the join quals fail, it
+	 * returns and we try ExecMergeNotMatched. Given that ExecMergeMatched
+	 * always make progress by following the update chain and we never switch
+	 * from ExecMergeNotMatched to ExecMergeMatched, there is no risk of a
+	 * livelock.
+	 */
+	if (matched)
+		matched = ExecMergeMatched(mtstate, estate, slot, junkfilter, tupleid);
+
+	/*
+	 * Either we were dealing with a NOT MATCHED tuple or ExecMergeNotMatched()
+	 * returned "false", indicating the previously MATCHED tuple is no longer a
+	 * matching tuple.
+	 */
+	if (!matched)
+		ExecMergeNotMatched(mtstate, estate, slot);
+}
+
+/*
+ * Check and execute the first qualifying MATCHED action. The current target
+ * tuple is identified by tupleid.
+ *
+ * We start from the first WHEN MATCHED action and check if the WHEN AND quals
+ * pass, if any. If the WHEN AND quals for the first action do not pass, we
+ * check the second, then the third and so on. If we reach to the end, no
+ * action is taken and we return true, indicating that no further action is
+ * required for this tuple.
+ *
+ * If we do find a qualifying action, then we attempt to execute the action.
+ *
+ * If the tuple is concurrently updated, EvalPlanQual is run with the updated
+ * tuple to recheck the join quals. Note that the additional quals associated
+ * with individual actions are evaluated separately by the MERGE code, while
+ * EvalPlanQual checks for the join quals. If EvalPlanQual tells us that the
+ * updated tuple still passes the join quals, then we restart from the first
+ * action to look for a qualifying action. Otherwise, we return false meaning
+ * that a NOT MATCHED action must now be executed for the current source tuple.
+ */
+static bool
+ExecMergeMatched(ModifyTableState *mtstate, EState *estate,
+				 TupleTableSlot *slot, JunkFilter *junkfilter,
+				 ItemPointer tupleid)
+{
+	ExprContext *econtext = mtstate->ps.ps_ExprContext;
+	bool		isNull;
+	List	   *mergeMatchedActionStates = NIL;
+	HeapUpdateFailureData hufd;
+	bool		tuple_updated,
+				tuple_deleted;
+	Buffer		buffer;
+	HeapTupleData tuple;
+	EPQState   *epqstate = &mtstate->mt_epqstate;
+	ResultRelInfo *saved_resultRelInfo;
+	ResultRelInfo *resultRelInfo = estate->es_result_relation_info;
+	ListCell   *l;
+	TupleTableSlot *saved_slot = slot;
+
+	if (mtstate->mt_partition_tuple_routing)
+	{
+		Datum		datum;
+		Oid			tableoid = InvalidOid;
+		PartitionTupleRouting *proute = mtstate->mt_partition_tuple_routing;
+
+		/*
+		 * In case of partitioned table, we fetch the tableoid while performing
+		 * MATCHED MERGE action.
+		 */
+		datum = ExecGetJunkAttribute(slot, junkfilter->jf_otherJunkAttNo,
+				&isNull);
+		Assert(!isNull);
+		tableoid = DatumGetObjectId(datum);
+
+		/*
+		 * If we're dealing with a MATCHED tuple, then tableoid must have been
+		 * set correctly. In case of partitioned table, we must now fetch the
+		 * correct result relation corresponding to the child table emitting
+		 * the matching target row. For normal table, there is just one result
+		 * relation and it must be the one emitting the matching row.
+		 */
+		resultRelInfo = ExecFindPartitionByOid(mtstate,
+				getTargetResultRelInfo(mtstate), proute, estate, tableoid);
+		Assert(resultRelInfo != NULL);
+	}
+
+	/*
+	 * Save the current information and work with the correct result relation.
+	 */
+	saved_resultRelInfo = resultRelInfo;
+	estate->es_result_relation_info = resultRelInfo;
+
+	/*
+	 * And get the correct action lists.
+	 */
+	mergeMatchedActionStates =
+		resultRelInfo->ri_mergeState->matchedActionStates;
+
+	/*
+	 * If there are not WHEN MATCHED actions, we are done.
+	 */
+	if (mergeMatchedActionStates == NIL)
+		return true;
+
+	/*
+	 * Make tuple and any needed join variables available to ExecQual and
+	 * ExecProject. The target's existing tuple is installed in the scantuple.
+	 * Again, this target relation's slot is required only in the case of a
+	 * MATCHED tuple and UPDATE/DELETE actions.
+	 */
+	if (mtstate->mt_partition_tuple_routing)
+		ExecSetSlotDescriptor(mtstate->mt_existing,
+				resultRelInfo->ri_RelationDesc->rd_att);
+	econtext->ecxt_scantuple = mtstate->mt_existing;
+	econtext->ecxt_innertuple = slot;
+	econtext->ecxt_outertuple = NULL;
+
+lmerge_matched:;
+	slot = saved_slot;
+
+	/*
+	 * UPDATE/DELETE is only invoked for matched rows. And we must have found
+	 * the tupleid of the target row in that case. We fetch using SnapshotAny
+	 * because we might get called again after EvalPlanQual returns us a new
+	 * tuple. This tuple may not be visible to our MVCC snapshot.
+	 */
+	Assert(tupleid != NULL);
+
+	tuple.t_self = *tupleid;
+	if (!heap_fetch(resultRelInfo->ri_RelationDesc, SnapshotAny, &tuple,
+					&buffer, true, NULL))
+		elog(ERROR, "Failed to fetch the target tuple");
+
+	/* Store target's existing tuple in the state's dedicated slot */
+	ExecStoreBufferHeapTuple(&tuple, mtstate->mt_existing, buffer);
+
+	foreach(l, mergeMatchedActionStates)
+	{
+		MergeActionState *action = (MergeActionState *) lfirst(l);
+
+		/*
+		 * Test condition, if any
+		 *
+		 * In the absence of a condition we perform the action unconditionally
+		 * (no need to check separately since ExecQual() will return true if
+		 * there are no conditions to evaluate).
+		 */
+		if (!ExecQual(action->whenqual, econtext))
+			continue;
+
+		/*
+		 * Check if the existing target tuple meet the USING checks of
+		 * UPDATE/DELETE RLS policies. If those checks fail, we throw an
+		 * error.
+		 *
+		 * The WITH CHECK quals are applied in ExecUpdate() and hence we need
+		 * not do anything special to handle them.
+		 *
+		 * NOTE: We must do this after WHEN quals are evaluated so that we
+		 * check policies only when they matter.
+		 */
+		if (resultRelInfo->ri_WithCheckOptions)
+		{
+			ExecWithCheckOptions(action->commandType == CMD_UPDATE ?
+								 WCO_RLS_MERGE_UPDATE_CHECK : WCO_RLS_MERGE_DELETE_CHECK,
+								 resultRelInfo,
+								 mtstate->mt_existing,
+								 mtstate->ps.state);
+		}
+
+		/* Perform stated action */
+		switch (action->commandType)
+		{
+			case CMD_UPDATE:
+
+				/*
+				 * We set up the projection earlier, so all we do here is
+				 * Project, no need for any other tasks prior to the
+				 * ExecUpdate.
+				 */
+				if (mtstate->mt_partition_tuple_routing)
+					ExecSetSlotDescriptor(mtstate->mt_mergeproj, action->tupDesc);
+				ExecProject(action->proj);
+
+				/*
+				 * We don't call ExecFilterJunk() because the projected tuple
+				 * using the UPDATE action's targetlist doesn't have a junk
+				 * attribute.
+				 */
+				slot = ExecUpdate(mtstate, tupleid, NULL,
+								  mtstate->mt_mergeproj,
+								  slot, epqstate, estate,
+								  &tuple_updated, &hufd,
+								  action, mtstate->canSetTag);
+				break;
+
+			case CMD_DELETE:
+				/* Nothing to Project for a DELETE action */
+				slot = ExecDelete(mtstate, tupleid, NULL,
+								  slot, epqstate, estate,
+								  false, mtstate->canSetTag,
+								  false /* changingPart */,
+								  &tuple_deleted, NULL,
+								  &hufd, action);
+
+				break;
+
+			default:
+				elog(ERROR, "unknown action in MERGE WHEN MATCHED clause");
+
+		}
+
+		/*
+		 * Check for any concurrent update/delete operation which may have
+		 * prevented our update/delete. We also check for situations where we
+		 * might be trying to update/delete the same tuple twice.
+		 */
+		if ((action->commandType == CMD_UPDATE && !tuple_updated) ||
+			(action->commandType == CMD_DELETE && !tuple_deleted))
+
+		{
+			switch (hufd.result)
+			{
+				case HeapTupleMayBeUpdated:
+					break;
+				case HeapTupleInvisible:
+
+					/*
+					 * This state should never be reached since the underlying
+					 * JOIN runs with a MVCC snapshot and EvalPlanQual runs
+					 * with a dirty snapshot. So such a row should have never
+					 * been returned for MERGE.
+					 */
+					elog(ERROR, "unexpected invisible tuple");
+					break;
+
+				case HeapTupleSelfUpdated:
+
+					/*
+					 * SQLStandard disallows this for MERGE.
+					 */
+					if (TransactionIdIsCurrentTransactionId(hufd.xmax))
+						ereport(ERROR,
+								(errcode(ERRCODE_CARDINALITY_VIOLATION),
+								 errmsg("MERGE command cannot affect row a second time"),
+								 errhint("Ensure that not more than one source row matches any one target row")));
+					/* This shouldn't happen */
+					elog(ERROR, "attempted to update or delete invisible tuple");
+					break;
+
+				case HeapTupleUpdated:
+
+					/*
+					 * The target tuple was concurrently updated/deleted by
+					 * some other transaction.
+					 *
+					 * If the current tuple is that last tuple in the update
+					 * chain, then we know that the tuple was concurrently
+					 * deleted. Just return and let the caller try NOT MATCHED
+					 * actions.
+					 *
+					 * If the current tuple was concurrently updated, then we
+					 * must run the EvalPlanQual() with the new version of the
+					 * tuple. If EvalPlanQual() does not return a tuple then
+					 * we switch to the NOT MATCHED list of actions.
+					 * If it does return a tuple and the join qual is
+					 * still satisfied, then we just need to recheck the
+					 * MATCHED actions, starting from the top, and execute the
+					 * first qualifying action.
+					 */
+					if (!ItemPointerEquals(tupleid, &hufd.ctid))
+					{
+						TupleTableSlot *epqslot;
+
+						/*
+						 * Since we generate a JOIN query with a target table
+						 * RTE different than the result relation RTE, we must
+						 * pass in the RTI of the relation used in the join
+						 * query and not the one from result relation.
+						 */
+						Assert(resultRelInfo->ri_mergeTargetRTI > 0);
+						epqslot = EvalPlanQual(estate,
+											   epqstate,
+											   resultRelInfo->ri_RelationDesc,
+											   GetEPQRangeTableIndex(resultRelInfo),
+											   LockTupleExclusive,
+											   &hufd.ctid,
+											   hufd.xmax);
+
+						if (!TupIsNull(epqslot))
+						{
+							/*
+							 * XXX Should we must use the junkfilter from the
+							 * resultRelInfo? If so, we must teach
+							 * ExecInitPartitionInfo to build one while
+							 * creating the partition-wise resultRelInfo.
+							 */
+							(void) ExecGetJunkAttribute(epqslot,
+														junkfilter->jf_junkAttNo,
+														&isNull);
+
+							/*
+							 * A non-NULL ctid means that we are still dealing
+							 * with MATCHED case. But we must retry from the
+							 * start with the updated tuple to ensure that the
+							 * first qualifying WHEN MATCHED action is
+							 * executed.
+							 *
+							 * We don't use the new slot returned by
+							 * EvalPlanQual because we anyways re-install the
+							 * new target tuple in econtext->ecxt_scantuple
+							 * before re-evaluating WHEN AND conditions and
+							 * re-projecting the update targetlists. The
+							 * source side tuple does not change and hence we
+							 * can safely continue to use the old slot.
+							 */
+							if (!isNull)
+							{
+								/*
+								 * Must update *tupleid to the TID of the
+								 * newer tuple found in the update chain.
+								 */
+								*tupleid = hufd.ctid;
+								ReleaseBuffer(buffer);
+								goto lmerge_matched;
+							}
+						}
+					}
+
+					/*
+					 * Tell the caller about the updated TID, restore the
+					 * state back and return.
+					 */
+					*tupleid = hufd.ctid;
+					estate->es_result_relation_info = saved_resultRelInfo;
+					ReleaseBuffer(buffer);
+					return false;
+
+				default:
+					break;
+
+			}
+		}
+
+		if (action->commandType == CMD_UPDATE && tuple_updated)
+			InstrCountNodeTuples2(&mtstate->ps, 1);
+		if (action->commandType == CMD_DELETE && tuple_deleted)
+			InstrCountNodeTuples3(&mtstate->ps, 1);
+
+		/*
+		 * We've activated one of the WHEN clauses, so we don't search
+		 * further. This is required behaviour, not an optimization.
+		 */
+		estate->es_result_relation_info = saved_resultRelInfo;
+		break;
+	}
+
+	ReleaseBuffer(buffer);
+
+	/*
+	 * Successfully executed an action or no qualifying action was found.
+	 */
+	return true;
+}
+
+/*
+ * Execute the first qualifying NOT MATCHED action.
+ */
+static void
+ExecMergeNotMatched(ModifyTableState *mtstate, EState *estate,
+					TupleTableSlot *slot)
+{
+	PartitionTupleRouting *proute = mtstate->mt_partition_tuple_routing;
+	ExprContext *econtext = mtstate->ps.ps_ExprContext;
+	List	   *mergeNotMatchedActionStates = NIL;
+	ResultRelInfo *resultRelInfo;
+	ListCell   *l;
+	TupleTableSlot	*myslot;
+
+	/*
+	 * We are dealing with NOT MATCHED tuple. Since for MERGE, the partition
+	 * tree is not expanded for the result relation, we continue to work with
+	 * the root of the partition tree.
+	 */
+	resultRelInfo = getTargetResultRelInfo(mtstate);
+
+	/*
+	 * For INSERT actions, root relation's merge action is OK since the
+	 * INSERT's targetlist and the WHEN conditions can only refer to the
+	 * source relation and hence it does not matter which result relation we
+	 * work with.
+	 */
+	mergeNotMatchedActionStates =
+		resultRelInfo->ri_mergeState->notMatchedActionStates;
+
+	/*
+	 * Make source tuple available to ExecQual and ExecProject. We don't need
+	 * the target tuple since the WHEN quals and the targetlist can't refer to
+	 * the target columns.
+	 */
+	econtext->ecxt_scantuple = NULL;
+	econtext->ecxt_innertuple = slot;
+	econtext->ecxt_outertuple = NULL;
+
+	foreach(l, mergeNotMatchedActionStates)
+	{
+		MergeActionState *action = (MergeActionState *) lfirst(l);
+
+		/*
+		 * Test condition, if any
+		 *
+		 * In the absence of a condition we perform the action unconditionally
+		 * (no need to check separately since ExecQual() will return true if
+		 * there are no conditions to evaluate).
+		 */
+		if (!ExecQual(action->whenqual, econtext))
+			continue;
+
+		/* Perform stated action */
+		switch (action->commandType)
+		{
+			case CMD_INSERT:
+
+				/*
+				 * We set up the projection earlier, so all we do here is
+				 * Project, no need for any other tasks prior to the
+				 * ExecInsert.
+				 */
+				if (mtstate->mt_partition_tuple_routing)
+					ExecSetSlotDescriptor(mtstate->mt_mergeproj, action->tupDesc);
+				ExecProject(action->proj);
+
+				/*
+				 * ExecPrepareTupleRouting may modify the passed-in slot. Hence
+				 * pass a local reference so that action->slot is not modified.
+				 */
+				myslot = mtstate->mt_mergeproj;
+
+				/* Prepare for tuple routing if needed. */
+				if (proute)
+					myslot = ExecPrepareTupleRouting(mtstate, estate, proute,
+												   resultRelInfo, myslot);
+				slot = ExecInsert(mtstate, myslot, slot,
+								  estate, action,
+								  mtstate->canSetTag);
+				/* Revert ExecPrepareTupleRouting's state change. */
+				if (proute)
+					estate->es_result_relation_info = resultRelInfo;
+				InstrCountNodeTuples1(&mtstate->ps, 1);
+				break;
+			case CMD_NOTHING:
+				/* Do Nothing */
+				break;
+			default:
+				elog(ERROR, "unknown action in MERGE WHEN NOT MATCHED clause");
+		}
+
+		break;
+	}
+}
+
+void
+ExecInitMerge(ModifyTableState *mtstate, EState *estate,
+			  ResultRelInfo *resultRelInfo)
+{
+	ListCell   *l;
+	ExprContext *econtext;
+	List	   *mergeMatchedActionStates = NIL;
+	List	   *mergeNotMatchedActionStates = NIL;
+	TupleDesc	relationDesc = resultRelInfo->ri_RelationDesc->rd_att;
+	ModifyTable *node = (ModifyTable *) mtstate->ps.plan;
+
+	if (node->mergeActionList == NIL)
+		return;
+
+	mtstate->mt_merge_subcommands = 0;
+
+	if (mtstate->ps.ps_ExprContext == NULL)
+		ExecAssignExprContext(estate, &mtstate->ps);
+
+	econtext = mtstate->ps.ps_ExprContext;
+
+	/* initialize slot for the existing tuple */
+	Assert(mtstate->mt_existing == NULL);
+	mtstate->mt_existing =
+		ExecInitExtraTupleSlot(mtstate->ps.state,
+							   mtstate->mt_partition_tuple_routing ?
+							   NULL : relationDesc, &TTSOpsBufferHeapTuple);
+
+	/* initialize slot for merge actions */
+	Assert(mtstate->mt_mergeproj == NULL);
+	mtstate->mt_mergeproj =
+		ExecInitExtraTupleSlot(mtstate->ps.state,
+							   mtstate->mt_partition_tuple_routing ?
+							   NULL : relationDesc, &TTSOpsHeapTuple);
+
+	/*
+	 * Create a MergeActionState for each action on the mergeActionList
+	 * and add it to either a list of matched actions or not-matched
+	 * actions.
+	 */
+	foreach(l, node->mergeActionList)
+	{
+		MergeAction *action = (MergeAction *) lfirst(l);
+		MergeActionState *action_state = makeNode(MergeActionState);
+		TupleDesc	tupDesc;
+
+		action_state->matched = action->matched;
+		action_state->commandType = action->commandType;
+		action_state->whenqual = ExecInitQual((List *) action->qual,
+				&mtstate->ps);
+
+		/* create target slot for this action's projection */
+		tupDesc = ExecTypeFromTL((List *) action->targetList);
+		action_state->tupDesc = tupDesc;
+
+		/* build action projection state */
+		action_state->proj =
+			ExecBuildProjectionInfo(action->targetList, econtext,
+					mtstate->mt_mergeproj, &mtstate->ps,
+					resultRelInfo->ri_RelationDesc->rd_att);
+
+		/*
+		 * We create two lists - one for WHEN MATCHED actions and one
+		 * for WHEN NOT MATCHED actions - and stick the
+		 * MergeActionState into the appropriate list.
+		 */
+		if (action_state->matched)
+			mergeMatchedActionStates =
+				lappend(mergeMatchedActionStates, action_state);
+		else
+			mergeNotMatchedActionStates =
+				lappend(mergeNotMatchedActionStates, action_state);
+
+		switch (action->commandType)
+		{
+			case CMD_INSERT:
+				ExecCheckPlanOutput(resultRelInfo->ri_RelationDesc,
+									action->targetList);
+				mtstate->mt_merge_subcommands |= MERGE_INSERT;
+				break;
+			case CMD_UPDATE:
+				ExecCheckPlanOutput(resultRelInfo->ri_RelationDesc,
+									action->targetList);
+				mtstate->mt_merge_subcommands |= MERGE_UPDATE;
+				break;
+			case CMD_DELETE:
+				mtstate->mt_merge_subcommands |= MERGE_DELETE;
+				break;
+			case CMD_NOTHING:
+				break;
+			default:
+				elog(ERROR, "unknown operation");
+				break;
+		}
+
+		resultRelInfo->ri_mergeState->matchedActionStates =
+					mergeMatchedActionStates;
+		resultRelInfo->ri_mergeState->notMatchedActionStates =
+					mergeNotMatchedActionStates;
+	}
+}
diff --git a/src/backend/executor/execPartition.c b/src/backend/executor/execPartition.c
index 179a501f30..cc6503f512 100644
--- a/src/backend/executor/execPartition.c
+++ b/src/backend/executor/execPartition.c
@@ -439,6 +439,190 @@ ExecFindPartition(ModifyTableState *mtstate,
 	}
 }
 
+/*
+ * Given OID of the partition leaf, return the index of the leaf at the current
+ * partition subroot. We ignore all non-leaf partitions. The caller must handle
+ * the case where the desired leaf partition is not a direct partition of the
+ * current subroot we're looking at.
+ */
+static ResultRelInfo *
+ExecSearchPartitionLeavesByOid(ModifyTableState *mtstate,
+					   ResultRelInfo *rootResultRelInfo,
+					   PartitionTupleRouting *proute,
+					   PartitionDispatch dispatch,
+					   EState *estate,
+					   Oid partoid)
+{
+	int partidx;
+	PartitionDesc partdesc = dispatch->partdesc;
+	ResultRelInfo *rri;
+
+	rri = NULL;
+	for (partidx = 0; partidx < partdesc->nparts; partidx++)
+	{
+		if (partdesc->oids[partidx] == partoid)
+		{
+			Assert(partdesc->is_leaf[partidx]);
+			break;
+		}
+	}
+
+	/*
+	 * If found, then do the necessary initialisation and return.
+	 */
+	if (partidx < partdesc->nparts)
+	{
+
+		/*
+		 * Look to see if we've already got a ResultRelInfo for this
+		 * partition.
+		 */
+		if (likely(dispatch->indexes[partidx] >= 0))
+		{
+			/* ResultRelInfo already built */
+			Assert(dispatch->indexes[partidx] < proute->num_partitions);
+			rri = proute->partitions[dispatch->indexes[partidx]];
+		}
+		else
+		{
+			bool		found = false;
+
+			/*
+			 * We have not yet set up a ResultRelInfo for this partition,
+			 * but if we have a subplan hash table, we might have one
+			 * there.  If not, we'll have to create one.
+			 */
+			if (proute->subplan_resultrel_htab)
+			{
+				Oid			partoid = partdesc->oids[partidx];
+				SubplanResultRelHashElem   *elem;
+
+				elem = hash_search(proute->subplan_resultrel_htab,
+						&partoid, HASH_FIND, NULL);
+				if (elem)
+				{
+					found = true;
+					rri = elem->rri;
+
+					/* Verify this ResultRelInfo allows INSERTs */
+					CheckValidResultRel(rri, CMD_INSERT);
+
+					/* Set up the PartitionRoutingInfo for it */
+					ExecInitRoutingInfo(mtstate, estate, proute, dispatch,
+							rri, partidx);
+				}
+			}
+
+			/* We need to create a new one. */
+			if (!found)
+				rri = ExecInitPartitionInfo(mtstate, estate, proute,
+						dispatch,
+						rootResultRelInfo, partidx);
+		}
+	}
+
+	/* Could be NULL if no matching partition found at the current level. */
+	return rri;
+}
+
+/*
+ * Helper function to recursively search a partition with the given OID in the
+ * partition hierarchy.
+ */
+static ResultRelInfo *
+ExecFindPartitionByOidRecurse(ModifyTableState *mtstate,
+					   ResultRelInfo *rootResultRelInfo,
+					   PartitionTupleRouting *proute,
+					   PartitionDispatch dispatch,
+					   EState *estate,
+					   Oid partoid)
+{
+	PartitionDispatch *pd = proute->partition_dispatch_info;
+	int partidx;
+	ResultRelInfo *rri;
+	PartitionDesc partdesc;
+
+	/*
+	 * If the desired partition is a leaf partition of the current (sub)-root
+	 * then we're done.
+	 */
+	rri = ExecSearchPartitionLeavesByOid(mtstate, rootResultRelInfo, proute,
+			dispatch, estate, partoid);
+	if (rri)
+		return rri;
+
+	/*
+	 * Else recursively search each of the subpartitions.
+	 */
+	partdesc = dispatch->partdesc;
+	for (partidx = 0; partidx < partdesc->nparts; partidx++)
+	{
+		PartitionDispatch subdispatch;
+
+		if (partdesc->is_leaf[partidx])
+			continue;
+
+		/*
+		 * Partition is a sub-partitioned table; get the PartitionDispatch
+		 */
+		if (likely(dispatch->indexes[partidx] >= 0))
+		{
+			/* Already built. */
+			Assert(dispatch->indexes[partidx] < proute->num_dispatch);
+
+			/*
+			 * Move down to the next partition level and search again
+			 * until we find a leaf partition that matches this tuple
+			 */
+			subdispatch = pd[dispatch->indexes[partidx]];
+		}
+		else
+		{
+			/*
+			 * Create the new PartitionDispatch.  We pass the current one
+			 * in as the parent PartitionDispatch
+			 */
+			subdispatch = ExecInitPartitionDispatchInfo(proute,
+					partdesc->oids[partidx],
+					dispatch, partidx);
+			Assert(dispatch->indexes[partidx] >= 0 &&
+					dispatch->indexes[partidx] < proute->num_dispatch);
+		}
+		rri = ExecFindPartitionByOidRecurse(mtstate, rootResultRelInfo, proute,
+				subdispatch, estate, partoid);
+		if (rri)
+			return rri;
+	}
+
+	return NULL;
+}
+
+/*
+ * Given OID of the partition leaf, return the index of the leaf in the
+ * partition hierarchy.
+ *
+ * XXX This is an O(N) operation and further optimization would be beneficial
+ */
+ResultRelInfo *
+ExecFindPartitionByOid(ModifyTableState *mtstate,
+					   ResultRelInfo *rootResultRelInfo,
+					   PartitionTupleRouting *proute,
+					   EState *estate,
+					   Oid partoid)
+{
+	PartitionDispatch  *pd = proute->partition_dispatch_info;
+	PartitionDispatch	dispatch = pd[0];
+	ResultRelInfo	   *rri;
+
+	/*
+	 * Recursively search starting at the root partition.
+	 */
+	rri = ExecFindPartitionByOidRecurse(mtstate, rootResultRelInfo, proute,
+			dispatch, estate, partoid);
+	Assert(rri);
+	return rri;
+}
+
 /*
  * ExecHashSubPlanResultRelsByOid
  *		Build a hash table to allow fast lookups of subplan ResultRelInfos by
@@ -522,6 +706,8 @@ ExecInitPartitionInfo(ModifyTableState *mtstate, EState *estate,
 					  rootrel,
 					  estate->es_instrument);
 
+	leaf_part_rri->ri_PartitionLeafIndex = partidx;
+
 	/*
 	 * Verify result relation is a valid target for an INSERT.  An UPDATE of a
 	 * partition-key becomes a DELETE+INSERT operation, so this check is still
@@ -847,6 +1033,96 @@ ExecInitPartitionInfo(ModifyTableState *mtstate, EState *estate,
 		lappend(estate->es_tuple_routing_result_relations,
 				leaf_part_rri);
 
+	/*
+	 * Initialize information about this partition that's needed to handle
+	 * MERGE.
+	 */
+	if (node && node->operation == CMD_MERGE)
+	{
+		TupleDesc	partrelDesc = RelationGetDescr(partrel);
+		TupleConversionMap *map =
+			leaf_part_rri->ri_PartitionInfo->pi_RootToPartitionMap;
+		int			firstVarno = mtstate->resultRelInfo[0].ri_RangeTableIndex;
+		Relation	firstResultRel = mtstate->resultRelInfo[0].ri_RelationDesc;
+
+		/*
+		 * If the root parent and partition have the same tuple
+		 * descriptor, just reuse the original MERGE state for partition.
+		 */
+		if (map == NULL)
+		{
+			leaf_part_rri->ri_mergeState = rootResultRelInfo->ri_mergeState;
+		}
+		else
+		{
+			/* Convert expressions contain partition's attnos. */
+			List	   *conv_tl, *conv_qual;
+			ListCell   *l;
+			List	   *matchedActionStates = NIL;
+			List	   *notMatchedActionStates = NIL;
+
+			foreach (l, node->mergeActionList)
+			{
+				MergeAction *action = lfirst_node(MergeAction, l);
+				MergeActionState *action_state = makeNode(MergeActionState);
+				TupleDesc	tupDesc;
+				ExprContext *econtext;
+
+				action_state->matched = action->matched;
+				action_state->commandType = action->commandType;
+
+				conv_qual = (List *) action->qual;
+				conv_qual = map_partition_varattnos(conv_qual,
+							firstVarno, partrel,
+							firstResultRel, NULL);
+
+				action_state->whenqual = ExecInitQual(conv_qual, &mtstate->ps);
+
+				conv_tl = (List *) action->targetList;
+				conv_tl = map_partition_varattnos(conv_tl,
+							firstVarno, partrel,
+							firstResultRel, NULL);
+
+				/* conv_tl may be NIL for DELETE action */
+				if (conv_tl != NIL)
+				{
+					conv_tl = adjust_partition_tlist( conv_tl, map);
+
+					tupDesc = ExecTypeFromTL(conv_tl);
+					action_state->tupDesc = tupDesc;
+
+					/* build action projection state */
+					econtext = mtstate->ps.ps_ExprContext;
+					action_state->proj =
+						ExecBuildProjectionInfo(conv_tl, econtext,
+								mtstate->mt_mergeproj,
+								&mtstate->ps,
+								partrelDesc);
+				}
+
+				if (action_state->matched)
+					matchedActionStates =
+						lappend(matchedActionStates, action_state);
+				else
+					notMatchedActionStates =
+						lappend(notMatchedActionStates, action_state);
+			}
+			leaf_part_rri->ri_mergeState->matchedActionStates =
+				matchedActionStates;
+			leaf_part_rri->ri_mergeState->notMatchedActionStates =
+				notMatchedActionStates;
+		}
+
+		/*
+		 * get_partition_dispatch_recurse() and expand_partitioned_rtentry()
+		 * fetch the leaf OIDs in the same order. So we can safely derive the
+		 * index of the merge target relation corresponding to this partition
+		 * by simply adding partidx + 1 to the root's merge target relation.
+		 */
+		leaf_part_rri->ri_mergeTargetRTI = node->mergeTargetRelation +
+			partidx + 1;
+	}
+
 	MemoryContextSwitchTo(oldcxt);
 
 	return leaf_part_rri;
@@ -910,7 +1186,8 @@ ExecInitRoutingInfo(ModifyTableState *mtstate,
 	 * from partition's rowtype to the root partition table's.
 	 */
 	if (mtstate &&
-		(mtstate->mt_transition_capture || mtstate->mt_oc_transition_capture))
+		(mtstate->mt_transition_capture || mtstate->mt_oc_transition_capture ||
+		 mtstate->operation == CMD_MERGE))
 	{
 		partrouteinfo->pi_PartitionToRootMap =
 			convert_tuples_by_name(RelationGetDescr(partRelInfo->ri_RelationDesc),
diff --git a/src/backend/executor/execReplication.c b/src/backend/executor/execReplication.c
index 5bd3bbc35e..29e0e81f73 100644
--- a/src/backend/executor/execReplication.c
+++ b/src/backend/executor/execReplication.c
@@ -479,7 +479,8 @@ ExecSimpleRelationUpdate(EState *estate, EPQState *epqstate,
 		resultRelInfo->ri_TrigDesc->trig_update_before_row)
 	{
 		slot = ExecBRUpdateTriggers(estate, epqstate, resultRelInfo,
-									&hsearchslot->tuple->t_self, NULL, slot);
+									&hsearchslot->tuple->t_self, NULL, slot,
+									NULL);
 
 		if (slot == NULL)		/* "do nothing" */
 			skip_tuple = true;
@@ -543,7 +544,7 @@ ExecSimpleRelationDelete(EState *estate, EPQState *epqstate,
 	{
 		skip_tuple = !ExecBRDeleteTriggers(estate, epqstate, resultRelInfo,
 										   &hsearchslot->tuple->t_self, NULL,
-										   NULL);
+										   NULL, NULL);
 	}
 
 	if (!skip_tuple)
diff --git a/src/backend/executor/instrument.c b/src/backend/executor/instrument.c
index 3ecb52c0b3..1222ac996b 100644
--- a/src/backend/executor/instrument.c
+++ b/src/backend/executor/instrument.c
@@ -152,7 +152,9 @@ InstrAggNode(Instrumentation *dst, Instrumentation *add)
 	dst->startup += add->startup;
 	dst->total += add->total;
 	dst->ntuples += add->ntuples;
-	dst->ntuples2 += add->ntuples2;
+	dst->node_ntuples1 += add->node_ntuples1;
+	dst->node_ntuples2 += add->node_ntuples2;
+	dst->node_ntuples3 += add->node_ntuples3;
 	dst->nloops += add->nloops;
 	dst->nfiltered1 += add->nfiltered1;
 	dst->nfiltered2 += add->nfiltered2;
diff --git a/src/backend/executor/nodeIndexonlyscan.c b/src/backend/executor/nodeIndexonlyscan.c
index d1201a1807..0c776b0107 100644
--- a/src/backend/executor/nodeIndexonlyscan.c
+++ b/src/backend/executor/nodeIndexonlyscan.c
@@ -162,7 +162,7 @@ IndexOnlyNext(IndexOnlyScanState *node)
 			/*
 			 * Rats, we have to visit the heap to check visibility.
 			 */
-			InstrCountTuples2(node, 1);
+			InstrCountNodeTuples1(node, 1);
 			tuple = index_fetch_heap(scandesc);
 			if (tuple == NULL)
 				continue;		/* no visible tuple, try next index entry */
diff --git a/src/backend/executor/nodeModifyTable.c b/src/backend/executor/nodeModifyTable.c
index 3c60bbcd9c..8567bd1f43 100644
--- a/src/backend/executor/nodeModifyTable.c
+++ b/src/backend/executor/nodeModifyTable.c
@@ -43,6 +43,7 @@
 #include "commands/trigger.h"
 #include "executor/execPartition.h"
 #include "executor/executor.h"
+#include "executor/execMerge.h"
 #include "executor/nodeModifyTable.h"
 #include "foreign/fdwapi.h"
 #include "miscadmin.h"
@@ -63,12 +64,6 @@ static bool ExecOnConflictUpdate(ModifyTableState *mtstate,
 					 EState *estate,
 					 bool canSetTag,
 					 TupleTableSlot **returning);
-static TupleTableSlot *ExecPrepareTupleRouting(ModifyTableState *mtstate,
-						EState *estate,
-						PartitionTupleRouting *proute,
-						ResultRelInfo *targetRelInfo,
-						TupleTableSlot *slot);
-static ResultRelInfo *getTargetResultRelInfo(ModifyTableState *node);
 static void ExecSetupChildParentMapForSubplan(ModifyTableState *mtstate);
 static TupleConversionMap *tupconv_map_for_subplan(ModifyTableState *node,
 						int whichplan);
@@ -85,7 +80,7 @@ static TupleConversionMap *tupconv_map_for_subplan(ModifyTableState *node,
  * The plan output is represented by its targetlist, because that makes
  * handling the dropped-column case easier.
  */
-static void
+void
 ExecCheckPlanOutput(Relation resultRel, List *targetList)
 {
 	TupleDesc	resultDesc = RelationGetDescr(resultRel);
@@ -253,11 +248,12 @@ ExecCheckTIDVisible(EState *estate,
  *		Returns RETURNING result if any, otherwise NULL.
  * ----------------------------------------------------------------
  */
-static TupleTableSlot *
+extern TupleTableSlot *
 ExecInsert(ModifyTableState *mtstate,
 		   TupleTableSlot *slot,
 		   TupleTableSlot *planSlot,
 		   EState *estate,
+		   MergeActionState *actionState,
 		   bool canSetTag)
 {
 	HeapTuple	tuple;
@@ -354,9 +350,17 @@ ExecInsert(ModifyTableState *mtstate,
 		 * partition, we should instead check UPDATE policies, because we are
 		 * executing policies defined on the target table, and not those
 		 * defined on the child partitions.
+		 *
+		 * If we're running MERGE, we refer to the action that we're executing
+		 * to know if we're doing an INSERT or UPDATE to a partition table.
 		 */
-		wco_kind = (mtstate->operation == CMD_UPDATE) ?
-			WCO_RLS_UPDATE_CHECK : WCO_RLS_INSERT_CHECK;
+		if (mtstate->operation == CMD_UPDATE)
+			wco_kind = WCO_RLS_UPDATE_CHECK;
+		else if (mtstate->operation == CMD_MERGE)
+			wco_kind = (actionState->commandType == CMD_UPDATE) ?
+				WCO_RLS_UPDATE_CHECK : WCO_RLS_INSERT_CHECK;
+		else
+			wco_kind = WCO_RLS_INSERT_CHECK;
 
 		/*
 		 * ExecWithCheckOptions() will skip any WCOs which are not of the kind
@@ -424,7 +428,7 @@ ExecInsert(ModifyTableState *mtstate,
 											 &conflictTid, planSlot, slot,
 											 estate, canSetTag, &returning))
 					{
-						InstrCountTuples2(&mtstate->ps, 1);
+						InstrCountNodeTuples1(&mtstate->ps, 1);
 						return returning;
 					}
 					else
@@ -439,7 +443,7 @@ ExecInsert(ModifyTableState *mtstate,
 					 */
 					Assert(onconflict == ONCONFLICT_NOTHING);
 					ExecCheckTIDVisible(estate, resultRelInfo, &conflictTid);
-					InstrCountTuples2(&mtstate->ps, 1);
+					InstrCountNodeTuples1(&mtstate->ps, 1);
 					return NULL;
 				}
 			}
@@ -588,10 +592,19 @@ ExecInsert(ModifyTableState *mtstate,
  *		part of an UPDATE of partition-key, then the slot returned by
  *		EvalPlanQual() is passed back using output parameter epqslot.
  *
+ *		MERGE passes actionState of the action it's currently executing;
+ *		regular DELETE passes NULL. This is used by ExecDelete to know if it's
+ *		being called from MERGE or regular DELETE operation.
+ *
+ *		If the DELETE fails because the tuple is concurrently updated/deleted
+ *		by this or some other transaction, hufdp is filled with the reason as
+ *		well as other important information. Currently only MERGE needs this
+ *		information.
+ *
  *		Returns RETURNING result if any, otherwise NULL.
  * ----------------------------------------------------------------
  */
-static TupleTableSlot *
+TupleTableSlot *
 ExecDelete(ModifyTableState *mtstate,
 		   ItemPointer tupleid,
 		   HeapTuple oldtuple,
@@ -602,7 +615,9 @@ ExecDelete(ModifyTableState *mtstate,
 		   bool canSetTag,
 		   bool changingPart,
 		   bool *tupleDeleted,
-		   TupleTableSlot **epqslot)
+		   TupleTableSlot **epqslot,
+		   HeapUpdateFailureData *hufdp,
+		   MergeActionState *actionState)
 {
 	ResultRelInfo *resultRelInfo;
 	Relation	resultRelationDesc;
@@ -614,6 +629,14 @@ ExecDelete(ModifyTableState *mtstate,
 	if (tupleDeleted)
 		*tupleDeleted = false;
 
+	/*
+	 * Initialize hufdp. Since the caller is only interested in the failure
+	 * status, initialize with the state that is used to indicate successful
+	 * operation.
+	 */
+	if (hufdp)
+		hufdp->result = HeapTupleMayBeUpdated;
+
 	/*
 	 * get information on the (current) result relation
 	 */
@@ -627,7 +650,7 @@ ExecDelete(ModifyTableState *mtstate,
 		bool		dodelete;
 
 		dodelete = ExecBRDeleteTriggers(estate, epqstate, resultRelInfo,
-										tupleid, oldtuple, epqslot);
+										tupleid, oldtuple, epqslot, hufdp);
 
 		if (!dodelete)			/* "do nothing" */
 			return NULL;
@@ -695,6 +718,15 @@ ldelete:;
 							 true /* wait for commit */ ,
 							 &hufd,
 							 changingPart);
+
+		/*
+		 * Copy the necessary information, if the caller has asked for it. We
+		 * must do this irrespective of whether the tuple was updated or
+		 * deleted.
+		 */
+		if (hufdp)
+			*hufdp = hufd;
+
 		switch (result)
 		{
 			case HeapTupleSelfUpdated:
@@ -729,7 +761,11 @@ ldelete:;
 							 errmsg("tuple to be updated was already modified by an operation triggered by the current command"),
 							 errhint("Consider using an AFTER trigger instead of a BEFORE trigger to propagate changes to other rows.")));
 
-				/* Else, already deleted by self; nothing to do */
+				/*
+				 * Else, already deleted by self; nothing to do but inform
+				 * MERGE about it anyways so that it can take necessary
+				 * action.
+				 */
 				return NULL;
 
 			case HeapTupleMayBeUpdated:
@@ -749,6 +785,14 @@ ldelete:;
 				{
 					TupleTableSlot *my_epqslot;
 
+					/*
+					 * If we're executing MERGE, then the onus of running
+					 * EvalPlanQual() and handling its outcome lies with the
+					 * caller.
+					 */
+					if (actionState != NULL)
+						return NULL;
+
 					my_epqslot = EvalPlanQual(estate,
 											  epqstate,
 											  resultRelationDesc,
@@ -773,7 +817,12 @@ ldelete:;
 							goto ldelete;
 					}
 				}
-				/* tuple already deleted; nothing to do */
+
+				/*
+				 * tuple already deleted; nothing to do. But MERGE might want
+				 * to handle it differently. We've already filled-in hufdp
+				 * with sufficient information for MERGE to look at.
+				 */
 				return NULL;
 
 			default:
@@ -901,10 +950,21 @@ ldelete:;
  *		foreign table triggers; it is NULL when the foreign table has
  *		no relevant triggers.
  *
+ *		MERGE passes actionState of the action it's currently executing;
+ *		regular UPDATE passes NULL. This is used by ExecUpdate to know if it's
+ *		being called from MERGE or regular UPDATE operation. ExecUpdate may
+ *		pass this information to ExecInsert if it ends up running DELETE+INSERT
+ *		for partition key updates.
+ *
+ *		If the UPDATE fails because the tuple is concurrently updated/deleted
+ *		by this or some other transaction, hufdp is filled with the reason as
+ *		well as other important information. Currently only MERGE needs this
+ *		information.
+ *
  *		Returns RETURNING result if any, otherwise NULL.
  * ----------------------------------------------------------------
  */
-static TupleTableSlot *
+extern TupleTableSlot *
 ExecUpdate(ModifyTableState *mtstate,
 		   ItemPointer tupleid,
 		   HeapTuple oldtuple,
@@ -912,6 +972,9 @@ ExecUpdate(ModifyTableState *mtstate,
 		   TupleTableSlot *planSlot,
 		   EPQState *epqstate,
 		   EState *estate,
+		   bool *tuple_updated,
+		   HeapUpdateFailureData *hufdp,
+		   MergeActionState *actionState,
 		   bool canSetTag)
 {
 	HeapTuple	tuple;
@@ -928,6 +991,17 @@ ExecUpdate(ModifyTableState *mtstate,
 	if (IsBootstrapProcessingMode())
 		elog(ERROR, "cannot UPDATE during bootstrap");
 
+	if (tuple_updated)
+		*tuple_updated = false;
+
+	/*
+	 * Initialize hufdp. Since the caller is only interested in the failure
+	 * status, initialize with the state that is used to indicate successful
+	 * operation.
+	 */
+	if (hufdp)
+		hufdp->result = HeapTupleMayBeUpdated;
+
 	/*
 	 * get the heap tuple out of the tuple table slot, making sure we have a
 	 * writable copy
@@ -945,7 +1019,7 @@ ExecUpdate(ModifyTableState *mtstate,
 		resultRelInfo->ri_TrigDesc->trig_update_before_row)
 	{
 		slot = ExecBRUpdateTriggers(estate, epqstate, resultRelInfo,
-									tupleid, oldtuple, slot);
+									tupleid, oldtuple, slot, hufdp);
 
 		if (slot == NULL)		/* "do nothing" */
 			return NULL;
@@ -991,7 +1065,6 @@ ExecUpdate(ModifyTableState *mtstate,
 	}
 	else
 	{
-		LockTupleMode lockmode;
 		bool		partition_constraint_failed;
 
 		/*
@@ -1072,7 +1145,8 @@ lreplace:;
 			 */
 			ExecDelete(mtstate, tupleid, oldtuple, planSlot, epqstate,
 					   estate, false, false /* canSetTag */ ,
-					   true /* changingPart */ , &tuple_deleted, &epqslot);
+					   true /* changingPart */ , &tuple_deleted,
+					   &epqslot, hufdp, actionState);
 
 			/*
 			 * For some reason if DELETE didn't happen (e.g. trigger prevented
@@ -1124,16 +1198,36 @@ lreplace:;
 				saved_tcs_map = mtstate->mt_transition_capture->tcs_map;
 
 			/*
-			 * resultRelInfo is one of the per-subplan resultRelInfos.  So we
-			 * should convert the tuple into root's tuple descriptor, since
-			 * ExecInsert() starts the search from root.  The tuple conversion
-			 * map list is in the order of mtstate->resultRelInfo[], so to
-			 * retrieve the one for this resultRel, we need to know the
-			 * position of the resultRel in mtstate->resultRelInfo[].
+			 * We should convert the tuple into root's tuple descriptor, since
+			 * ExecInsert() starts the search from root. To do that, we need to
+			 * retrieve the tuple conversion map for this resultRelInfo.
+			 *
+			 * If we're running MERGE then resultRelInfo is per-partition
+			 * resultRelInfo as initialized in ExecInitPartitionInfo(). Note
+			 * that we don't expand inheritance for the resultRelation in case
+			 * of MERGE and hence there is just one subplan. Whereas for
+			 * regular UPDATE, resultRelInfo is one of the per-subplan
+			 * resultRelInfos. In either case the position of this partition in
+			 * tracked in ri_PartitionLeafIndex;
+			 *
+			 * Retrieve the map either by looking at the resultRelInfo's
+			 * position in mtstate->resultRelInfo[] (for UPDATE) or by simply
+			 * using the map already setup in the resultRelInfo (for MERGE).
+			 *
+			 * XXX Can the non-MERGE path also not use the
+			 * pi_PartitionToRootMap?
 			 */
-			map_index = resultRelInfo - mtstate->resultRelInfo;
-			Assert(map_index >= 0 && map_index < mtstate->mt_nplans);
-			tupconv_map = tupconv_map_for_subplan(mtstate, map_index);
+			if (mtstate->operation == CMD_MERGE)
+			{
+				tupconv_map =
+					resultRelInfo->ri_PartitionInfo->pi_PartitionToRootMap;
+			}
+			else
+			{
+				map_index = resultRelInfo - mtstate->resultRelInfo;
+				Assert(map_index >= 0 && map_index < mtstate->mt_nplans);
+				tupconv_map = tupconv_map_for_subplan(mtstate, map_index);
+			}
 			if (tupconv_map != NULL)
 				slot = execute_attr_map_slot(tupconv_map->attrMap,
 											 slot,
@@ -1143,12 +1237,16 @@ lreplace:;
 			 * Prepare for tuple routing, making it look like we're inserting
 			 * into the root.
 			 */
-			Assert(mtstate->rootResultRelInfo != NULL);
 			slot = ExecPrepareTupleRouting(mtstate, estate, proute,
-										   mtstate->rootResultRelInfo, slot);
+										   getTargetResultRelInfo(mtstate),
+										   slot);
 
 			ret_slot = ExecInsert(mtstate, slot, planSlot,
-								  estate, canSetTag);
+								  estate, actionState, canSetTag);
+
+			/* Update is successful. */
+			if (tuple_updated)
+				*tuple_updated = true;
 
 			/* Revert ExecPrepareTupleRouting's node change. */
 			estate->es_result_relation_info = resultRelInfo;
@@ -1183,7 +1281,16 @@ lreplace:;
 							 estate->es_output_cid,
 							 estate->es_crosscheck_snapshot,
 							 true /* wait for commit */ ,
-							 &hufd, &lockmode);
+							 &hufd);
+
+		/*
+		 * Copy the necessary information, if the caller has asked for it. We
+		 * must do this irrespective of whether the tuple was updated or
+		 * deleted.
+		 */
+		if (hufdp)
+			*hufdp = hufd;
+
 		switch (result)
 		{
 			case HeapTupleSelfUpdated:
@@ -1237,22 +1344,37 @@ lreplace:;
 				{
 					TupleTableSlot *epqslot;
 
+					/*
+					 * If we're executing MERGE, then the onus of running
+					 * EvalPlanQual() and handling its outcome lies with the
+					 * caller.
+					 */
+					if (actionState != NULL)
+						return NULL;
+
+					/* Regular UPDATE path. */
 					epqslot = EvalPlanQual(estate,
 										   epqstate,
 										   resultRelationDesc,
-										   resultRelInfo->ri_RangeTableIndex,
-										   lockmode,
+										   GetEPQRangeTableIndex(resultRelInfo),
+										   hufd.lockmode,
 										   &hufd.ctid,
 										   hufd.xmax);
 					if (!TupIsNull(epqslot))
 					{
 						*tupleid = hufd.ctid;
+						/* Normal UPDATE path */
 						slot = ExecFilterJunk(resultRelInfo->ri_junkFilter, epqslot);
 						tuple = ExecFetchSlotHeapTuple(slot, true, NULL);
 						goto lreplace;
 					}
 				}
-				/* tuple already deleted; nothing to do */
+
+				/*
+				 * tuple already deleted; nothing to do. But MERGE might want
+				 * to handle it differently. We've already filled-in hufdp
+				 * with sufficient information for MERGE to look at.
+				 */
 				return NULL;
 
 			default:
@@ -1281,6 +1403,9 @@ lreplace:;
 												   estate, false, NULL, NIL);
 	}
 
+	if (tuple_updated)
+		*tuple_updated = true;
+
 	if (canSetTag)
 		(estate->es_processed)++;
 
@@ -1375,9 +1500,9 @@ ExecOnConflictUpdate(ModifyTableState *mtstate,
 			 * there's no historical behavior to break.
 			 *
 			 * It is the user's responsibility to prevent this situation from
-			 * occurring.  These problems are why SQL-2003 similarly specifies
-			 * that for SQL MERGE, an exception must be raised in the event of
-			 * an attempt to update the same row twice.
+			 * occurring.  These problems are why SQL Standard similarly
+			 * specifies that for SQL MERGE, an exception must be raised in
+			 * the event of an attempt to update the same row twice.
 			 */
 			if (TransactionIdIsCurrentTransactionId(HeapTupleHeaderGetXmin(tuple.t_data)))
 				ereport(ERROR,
@@ -1503,7 +1628,7 @@ ExecOnConflictUpdate(ModifyTableState *mtstate,
 	*returning = ExecUpdate(mtstate, &tuple.t_self, NULL,
 							mtstate->mt_conflproj, planSlot,
 							&mtstate->mt_epqstate, mtstate->ps.state,
-							canSetTag);
+							NULL, NULL, NULL, canSetTag);
 
 	ReleaseBuffer(buffer);
 	return true;
@@ -1541,6 +1666,14 @@ fireBSTriggers(ModifyTableState *node)
 		case CMD_DELETE:
 			ExecBSDeleteTriggers(node->ps.state, resultRelInfo);
 			break;
+		case CMD_MERGE:
+			if (node->mt_merge_subcommands & MERGE_INSERT)
+				ExecBSInsertTriggers(node->ps.state, resultRelInfo);
+			if (node->mt_merge_subcommands & MERGE_UPDATE)
+				ExecBSUpdateTriggers(node->ps.state, resultRelInfo);
+			if (node->mt_merge_subcommands & MERGE_DELETE)
+				ExecBSDeleteTriggers(node->ps.state, resultRelInfo);
+			break;
 		default:
 			elog(ERROR, "unknown operation");
 			break;
@@ -1556,7 +1689,7 @@ fireBSTriggers(ModifyTableState *node)
  *   be converted.
  * - the root partitioned table.
  */
-static ResultRelInfo *
+ResultRelInfo *
 getTargetResultRelInfo(ModifyTableState *node)
 {
 	/*
@@ -1596,6 +1729,17 @@ fireASTriggers(ModifyTableState *node)
 			ExecASDeleteTriggers(node->ps.state, resultRelInfo,
 								 node->mt_transition_capture);
 			break;
+		case CMD_MERGE:
+			if (node->mt_merge_subcommands & MERGE_DELETE)
+				ExecASDeleteTriggers(node->ps.state, resultRelInfo,
+									 node->mt_transition_capture);
+			if (node->mt_merge_subcommands & MERGE_UPDATE)
+				ExecASUpdateTriggers(node->ps.state, resultRelInfo,
+									 node->mt_transition_capture);
+			if (node->mt_merge_subcommands & MERGE_INSERT)
+				ExecASInsertTriggers(node->ps.state, resultRelInfo,
+									 node->mt_transition_capture);
+			break;
 		default:
 			elog(ERROR, "unknown operation");
 			break;
@@ -1658,7 +1802,7 @@ ExecSetupTransitionCaptureState(ModifyTableState *mtstate, EState *estate)
  *
  * Returns a slot holding the tuple of the partition rowtype.
  */
-static TupleTableSlot *
+TupleTableSlot *
 ExecPrepareTupleRouting(ModifyTableState *mtstate,
 						EState *estate,
 						PartitionTupleRouting *proute,
@@ -1904,6 +2048,7 @@ ExecModifyTable(PlanState *pstate)
 		{
 			/* advance to next subplan if any */
 			node->mt_whichplan++;
+
 			if (node->mt_whichplan < node->mt_nplans)
 			{
 				resultRelInfo++;
@@ -1961,6 +2106,12 @@ ExecModifyTable(PlanState *pstate)
 		EvalPlanQualSetSlot(&node->mt_epqstate, planSlot);
 		slot = planSlot;
 
+		if (operation == CMD_MERGE)
+		{
+			ExecMerge(node, estate, slot, junkfilter, resultRelInfo);
+			continue;
+		}
+
 		tupleid = NULL;
 		oldtuple = NULL;
 		if (junkfilter != NULL)
@@ -2042,20 +2193,22 @@ ExecModifyTable(PlanState *pstate)
 					slot = ExecPrepareTupleRouting(node, estate, proute,
 												   resultRelInfo, slot);
 				slot = ExecInsert(node, slot, planSlot,
-								  estate, node->canSetTag);
+								  estate, NULL, node->canSetTag);
 				/* Revert ExecPrepareTupleRouting's state change. */
 				if (proute)
 					estate->es_result_relation_info = resultRelInfo;
 				break;
 			case CMD_UPDATE:
 				slot = ExecUpdate(node, tupleid, oldtuple, slot, planSlot,
-								  &node->mt_epqstate, estate, node->canSetTag);
+								  &node->mt_epqstate, estate,
+								  NULL, NULL, NULL, node->canSetTag);
 				break;
 			case CMD_DELETE:
 				slot = ExecDelete(node, tupleid, oldtuple, planSlot,
 								  &node->mt_epqstate, estate,
 								  true, node->canSetTag,
-								  false /* changingPart */ , NULL, NULL);
+								  false /* changingPart */ , NULL, NULL,
+								  NULL, NULL);
 				break;
 			default:
 				elog(ERROR, "unknown operation");
@@ -2102,7 +2255,15 @@ ExecInitModifyTable(ModifyTable *node, EState *estate, int eflags)
 	ListCell   *l;
 	int			i;
 	Relation	rel;
-	bool		update_tuple_routing_needed = node->partColsUpdated;
+
+	/* 
+	 * XXX For MERGE, we haven't yet figured out a nice way to get the info
+	 * about partition column updates since the partition tree is not expanded
+	 * for the target relation. Just a hack for now to ensure required states
+	 * are created.
+	 */
+	bool		update_tuple_routing_needed = node->partColsUpdated ||
+											  (node->operation == CMD_MERGE);
 
 	/* check for unsupported flags */
 	Assert(!(eflags & (EXEC_FLAG_BACKWARD | EXEC_FLAG_MARK)));
@@ -2146,6 +2307,16 @@ ExecInitModifyTable(ModifyTable *node, EState *estate, int eflags)
 	saved_resultRelInfo = estate->es_result_relation_info;
 
 	resultRelInfo = mtstate->resultRelInfo;
+
+	/*
+	 * mergeTargetRelation must be set if we're running MERGE and mustn't be
+	 * set if we're not.
+	 */
+	Assert(operation != CMD_MERGE || node->mergeTargetRelation > 0);
+	Assert(operation == CMD_MERGE || node->mergeTargetRelation == 0);
+
+	resultRelInfo->ri_mergeTargetRTI = node->mergeTargetRelation;
+
 	i = 0;
 	foreach(l, node->plans)
 	{
@@ -2227,7 +2398,8 @@ ExecInitModifyTable(ModifyTable *node, EState *estate, int eflags)
 	 * partition key.
 	 */
 	if (rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE &&
-		(operation == CMD_INSERT || update_tuple_routing_needed))
+		(operation == CMD_INSERT || operation == CMD_MERGE ||
+		 update_tuple_routing_needed))
 		mtstate->mt_partition_tuple_routing =
 			ExecSetupPartitionTupleRouting(mtstate, rel);
 
@@ -2238,6 +2410,15 @@ ExecInitModifyTable(ModifyTable *node, EState *estate, int eflags)
 	if (!(eflags & EXEC_FLAG_EXPLAIN_ONLY))
 		ExecSetupTransitionCaptureState(mtstate, estate);
 
+	/*
+	 * If we are doing MERGE then setup child-parent mapping. This will be
+	 * required in case we end up doing a partition-key update, triggering a
+	 * tuple routing.
+	 */
+	if (mtstate->operation == CMD_MERGE &&
+		mtstate->mt_partition_tuple_routing != NULL)
+		ExecSetupChildParentMapForSubplan(mtstate);
+
 	/*
 	 * Construct mapping from each of the per-subplan partition attnos to the
 	 * root attno.  This is required when during update row movement the tuple
@@ -2434,6 +2615,10 @@ ExecInitModifyTable(ModifyTable *node, EState *estate, int eflags)
 		}
 	}
 
+	resultRelInfo = getTargetResultRelInfo(mtstate);
+	if (mtstate->operation == CMD_MERGE)
+		ExecInitMerge(mtstate, estate, resultRelInfo);
+
 	/* select first subplan */
 	mtstate->mt_whichplan = 0;
 	subplan = (Plan *) linitial(node->plans);
@@ -2447,7 +2632,7 @@ ExecInitModifyTable(ModifyTable *node, EState *estate, int eflags)
 	 * --- no need to look first.  Typically, this will be a 'ctid' or
 	 * 'wholerow' attribute, but in the case of a foreign data wrapper it
 	 * might be a set of junk attributes sufficient to identify the remote
-	 * row.
+	 * row. We follow this logic for MERGE, so it always has a junk attributes.
 	 *
 	 * If there are multiple result relations, each one needs its own junk
 	 * filter.  Note multiple rels are only possible for UPDATE/DELETE, so we
@@ -2475,6 +2660,7 @@ ExecInitModifyTable(ModifyTable *node, EState *estate, int eflags)
 				break;
 			case CMD_UPDATE:
 			case CMD_DELETE:
+			case CMD_MERGE:
 				junk_filter_needed = true;
 				break;
 			default:
@@ -2490,6 +2676,7 @@ ExecInitModifyTable(ModifyTable *node, EState *estate, int eflags)
 				JunkFilter *j;
 
 				subplan = mtstate->mt_plans[i]->plan;
+
 				if (operation == CMD_INSERT || operation == CMD_UPDATE)
 					ExecCheckPlanOutput(resultRelInfo->ri_RelationDesc,
 										subplan->targetlist);
@@ -2498,7 +2685,9 @@ ExecInitModifyTable(ModifyTable *node, EState *estate, int eflags)
 									   ExecInitExtraTupleSlot(estate, NULL,
 															  &TTSOpsHeapTuple));
 
-				if (operation == CMD_UPDATE || operation == CMD_DELETE)
+				if (operation == CMD_UPDATE ||
+					operation == CMD_DELETE ||
+					operation == CMD_MERGE)
 				{
 					/* For UPDATE/DELETE, find the appropriate junk attr now */
 					char		relkind;
@@ -2511,6 +2700,15 @@ ExecInitModifyTable(ModifyTable *node, EState *estate, int eflags)
 						j->jf_junkAttNo = ExecFindJunkAttribute(j, "ctid");
 						if (!AttributeNumberIsValid(j->jf_junkAttNo))
 							elog(ERROR, "could not find junk ctid column");
+
+						if (operation == CMD_MERGE &&
+							relkind == RELKIND_PARTITIONED_TABLE)
+						{
+							j->jf_otherJunkAttNo = ExecFindJunkAttribute(j, "tableoid");
+							if (!AttributeNumberIsValid(j->jf_otherJunkAttNo))
+								elog(ERROR, "could not find junk tableoid column");
+
+						}
 					}
 					else if (relkind == RELKIND_FOREIGN_TABLE)
 					{
diff --git a/src/backend/executor/spi.c b/src/backend/executor/spi.c
index ad726676d8..c640f766ad 100644
--- a/src/backend/executor/spi.c
+++ b/src/backend/executor/spi.c
@@ -2451,6 +2451,9 @@ _SPI_pquery(QueryDesc *queryDesc, bool fire_triggers, uint64 tcount)
 			else
 				res = SPI_OK_UPDATE;
 			break;
+		case CMD_MERGE:
+			res = SPI_OK_MERGE;
+			break;
 		default:
 			return SPI_ERROR_OPUNKNOWN;
 	}
diff --git a/src/backend/nodes/copyfuncs.c b/src/backend/nodes/copyfuncs.c
index db49968409..7ae694eed3 100644
--- a/src/backend/nodes/copyfuncs.c
+++ b/src/backend/nodes/copyfuncs.c
@@ -206,6 +206,7 @@ _copyModifyTable(const ModifyTable *from)
 	COPY_SCALAR_FIELD(rootRelation);
 	COPY_SCALAR_FIELD(partColsUpdated);
 	COPY_NODE_FIELD(resultRelations);
+	COPY_SCALAR_FIELD(mergeTargetRelation);
 	COPY_SCALAR_FIELD(resultRelIndex);
 	COPY_SCALAR_FIELD(rootResultRelIndex);
 	COPY_NODE_FIELD(plans);
@@ -221,6 +222,8 @@ _copyModifyTable(const ModifyTable *from)
 	COPY_NODE_FIELD(onConflictWhere);
 	COPY_SCALAR_FIELD(exclRelRTI);
 	COPY_NODE_FIELD(exclRelTlist);
+	COPY_NODE_FIELD(mergeSourceTargetList);
+	COPY_NODE_FIELD(mergeActionList);
 
 	return newnode;
 }
@@ -2195,6 +2198,20 @@ _copyOnConflictExpr(const OnConflictExpr *from)
 	return newnode;
 }
 
+static MergeAction *
+_copyMergeAction(const MergeAction *from)
+{
+	MergeAction *newnode = makeNode(MergeAction);
+
+	COPY_SCALAR_FIELD(matched);
+	COPY_SCALAR_FIELD(commandType);
+	COPY_SCALAR_FIELD(override);
+	COPY_NODE_FIELD(qual);
+	COPY_NODE_FIELD(targetList);
+
+	return newnode;
+}
+
 /* ****************************************************************
  *						relation.h copy functions
  *
@@ -3025,6 +3042,9 @@ _copyQuery(const Query *from)
 	COPY_NODE_FIELD(setOperations);
 	COPY_NODE_FIELD(constraintDeps);
 	COPY_NODE_FIELD(withCheckOptions);
+	COPY_SCALAR_FIELD(mergeTarget_relation);
+	COPY_NODE_FIELD(mergeSourceTargetList);
+	COPY_NODE_FIELD(mergeActionList);
 	COPY_LOCATION_FIELD(stmt_location);
 	COPY_LOCATION_FIELD(stmt_len);
 
@@ -3088,6 +3108,35 @@ _copyUpdateStmt(const UpdateStmt *from)
 	return newnode;
 }
 
+static MergeStmt *
+_copyMergeStmt(const MergeStmt *from)
+{
+	MergeStmt  *newnode = makeNode(MergeStmt);
+
+	COPY_NODE_FIELD(relation);
+	COPY_NODE_FIELD(source_relation);
+	COPY_NODE_FIELD(join_condition);
+	COPY_NODE_FIELD(mergeWhenClauses);
+	COPY_NODE_FIELD(withClause);
+
+	return newnode;
+}
+
+static MergeWhenClause *
+_copyMergeWhenClause(const MergeWhenClause *from)
+{
+	MergeWhenClause *newnode = makeNode(MergeWhenClause);
+
+	COPY_SCALAR_FIELD(matched);
+	COPY_SCALAR_FIELD(commandType);
+	COPY_NODE_FIELD(condition);
+	COPY_NODE_FIELD(targetList);
+	COPY_NODE_FIELD(cols);
+	COPY_NODE_FIELD(values);
+	COPY_SCALAR_FIELD(override);
+	return newnode;
+}
+
 static SelectStmt *
 _copySelectStmt(const SelectStmt *from)
 {
@@ -5086,6 +5135,9 @@ copyObjectImpl(const void *from)
 		case T_OnConflictExpr:
 			retval = _copyOnConflictExpr(from);
 			break;
+		case T_MergeAction:
+			retval = _copyMergeAction(from);
+			break;
 
 			/*
 			 * RELATION NODES
@@ -5161,6 +5213,12 @@ copyObjectImpl(const void *from)
 		case T_UpdateStmt:
 			retval = _copyUpdateStmt(from);
 			break;
+		case T_MergeStmt:
+			retval = _copyMergeStmt(from);
+			break;
+		case T_MergeWhenClause:
+			retval = _copyMergeWhenClause(from);
+			break;
 		case T_SelectStmt:
 			retval = _copySelectStmt(from);
 			break;
diff --git a/src/backend/nodes/equalfuncs.c b/src/backend/nodes/equalfuncs.c
index 3a084b4d1f..59bb51599c 100644
--- a/src/backend/nodes/equalfuncs.c
+++ b/src/backend/nodes/equalfuncs.c
@@ -812,6 +812,18 @@ _equalOnConflictExpr(const OnConflictExpr *a, const OnConflictExpr *b)
 	return true;
 }
 
+
+static bool
+_equalMergeAction(const MergeAction *a, const MergeAction *b)
+{
+	COMPARE_SCALAR_FIELD(matched);
+	COMPARE_SCALAR_FIELD(commandType);
+	COMPARE_SCALAR_FIELD(override);
+	COMPARE_NODE_FIELD(qual);
+	COMPARE_NODE_FIELD(targetList);
+
+	return true;
+}
 /*
  * Stuff from relation.h
  */
@@ -977,6 +989,8 @@ _equalQuery(const Query *a, const Query *b)
 	COMPARE_NODE_FIELD(setOperations);
 	COMPARE_NODE_FIELD(constraintDeps);
 	COMPARE_NODE_FIELD(withCheckOptions);
+	COMPARE_NODE_FIELD(mergeSourceTargetList);
+	COMPARE_NODE_FIELD(mergeActionList);
 	COMPARE_LOCATION_FIELD(stmt_location);
 	COMPARE_LOCATION_FIELD(stmt_len);
 
@@ -1032,6 +1046,32 @@ _equalUpdateStmt(const UpdateStmt *a, const UpdateStmt *b)
 	return true;
 }
 
+static bool
+_equalMergeStmt(const MergeStmt *a, const MergeStmt *b)
+{
+	COMPARE_NODE_FIELD(relation);
+	COMPARE_NODE_FIELD(source_relation);
+	COMPARE_NODE_FIELD(join_condition);
+	COMPARE_NODE_FIELD(mergeWhenClauses);
+	COMPARE_NODE_FIELD(withClause);
+
+	return true;
+}
+
+static bool
+_equalMergeWhenClause(const MergeWhenClause *a, const MergeWhenClause *b)
+{
+	COMPARE_SCALAR_FIELD(matched);
+	COMPARE_SCALAR_FIELD(commandType);
+	COMPARE_NODE_FIELD(condition);
+	COMPARE_NODE_FIELD(targetList);
+	COMPARE_NODE_FIELD(cols);
+	COMPARE_NODE_FIELD(values);
+	COMPARE_SCALAR_FIELD(override);
+
+	return true;
+}
+
 static bool
 _equalSelectStmt(const SelectStmt *a, const SelectStmt *b)
 {
@@ -3157,6 +3197,9 @@ equal(const void *a, const void *b)
 		case T_OnConflictExpr:
 			retval = _equalOnConflictExpr(a, b);
 			break;
+		case T_MergeAction:
+			retval = _equalMergeAction(a, b);
+			break;
 		case T_JoinExpr:
 			retval = _equalJoinExpr(a, b);
 			break;
@@ -3222,6 +3265,12 @@ equal(const void *a, const void *b)
 		case T_UpdateStmt:
 			retval = _equalUpdateStmt(a, b);
 			break;
+		case T_MergeStmt:
+			retval = _equalMergeStmt(a, b);
+			break;
+		case T_MergeWhenClause:
+			retval = _equalMergeWhenClause(a, b);
+			break;
 		case T_SelectStmt:
 			retval = _equalSelectStmt(a, b);
 			break;
diff --git a/src/backend/nodes/nodeFuncs.c b/src/backend/nodes/nodeFuncs.c
index a10014f755..4c309d236a 100644
--- a/src/backend/nodes/nodeFuncs.c
+++ b/src/backend/nodes/nodeFuncs.c
@@ -2146,6 +2146,16 @@ expression_tree_walker(Node *node,
 					return true;
 			}
 			break;
+		case T_MergeAction:
+			{
+				MergeAction *action = (MergeAction *) node;
+
+				if (walker(action->targetList, context))
+					return true;
+				if (walker(action->qual, context))
+					return true;
+			}
+			break;
 		case T_PartitionPruneStepOp:
 			{
 				PartitionPruneStepOp *opstep = (PartitionPruneStepOp *) node;
@@ -2266,6 +2276,10 @@ query_tree_walker(Query *query,
 		return true;
 	if (walker((Node *) query->onConflict, context))
 		return true;
+	if (walker((Node *) query->mergeSourceTargetList, context))
+		return true;
+	if (walker((Node *) query->mergeActionList, context))
+		return true;
 	if (walker((Node *) query->returningList, context))
 		return true;
 	if (walker((Node *) query->jointree, context))
@@ -2943,6 +2957,18 @@ expression_tree_mutator(Node *node,
 				return (Node *) newnode;
 			}
 			break;
+		case T_MergeAction:
+			{
+				MergeAction *action = (MergeAction *) node;
+				MergeAction *newnode;
+
+				FLATCOPY(newnode, action, MergeAction);
+				MUTATE(newnode->qual, action->qual, Node *);
+				MUTATE(newnode->targetList, action->targetList, List *);
+
+				return (Node *) newnode;
+			}
+			break;
 		case T_PartitionPruneStepOp:
 			{
 				PartitionPruneStepOp *opstep = (PartitionPruneStepOp *) node;
@@ -3108,6 +3134,8 @@ query_tree_mutator(Query *query,
 	MUTATE(query->targetList, query->targetList, List *);
 	MUTATE(query->withCheckOptions, query->withCheckOptions, List *);
 	MUTATE(query->onConflict, query->onConflict, OnConflictExpr *);
+	MUTATE(query->mergeSourceTargetList, query->mergeSourceTargetList, List *);
+	MUTATE(query->mergeActionList, query->mergeActionList, List *);
 	MUTATE(query->returningList, query->returningList, List *);
 	MUTATE(query->jointree, query->jointree, FromExpr *);
 	MUTATE(query->setOperations, query->setOperations, Node *);
@@ -3249,9 +3277,9 @@ query_or_expression_tree_mutator(Node *node,
  * boundaries: we descend to everything that's possibly interesting.
  *
  * Currently, the node type coverage here extends only to DML statements
- * (SELECT/INSERT/UPDATE/DELETE) and nodes that can appear in them, because
- * this is used mainly during analysis of CTEs, and only DML statements can
- * appear in CTEs.
+ * (SELECT/INSERT/UPDATE/DELETE/MERGE) and nodes that can appear in them,
+ * because this is used mainly during analysis of CTEs, and only DML
+ * statements can appear in CTEs.
  */
 bool
 raw_expression_tree_walker(Node *node,
@@ -3431,6 +3459,36 @@ raw_expression_tree_walker(Node *node,
 					return true;
 			}
 			break;
+		case T_MergeStmt:
+			{
+				MergeStmt  *stmt = (MergeStmt *) node;
+
+				if (walker(stmt->relation, context))
+					return true;
+				if (walker(stmt->source_relation, context))
+					return true;
+				if (walker(stmt->join_condition, context))
+					return true;
+				if (walker(stmt->mergeWhenClauses, context))
+					return true;
+				if (walker(stmt->withClause, context))
+					return true;
+			}
+			break;
+		case T_MergeWhenClause:
+			{
+				MergeWhenClause *mergeWhenClause = (MergeWhenClause *) node;
+
+				if (walker(mergeWhenClause->condition, context))
+					return true;
+				if (walker(mergeWhenClause->targetList, context))
+					return true;
+				if (walker(mergeWhenClause->cols, context))
+					return true;
+				if (walker(mergeWhenClause->values, context))
+					return true;
+			}
+			break;
 		case T_SelectStmt:
 			{
 				SelectStmt *stmt = (SelectStmt *) node;
diff --git a/src/backend/nodes/outfuncs.c b/src/backend/nodes/outfuncs.c
index f0c396530d..c1b829ee81 100644
--- a/src/backend/nodes/outfuncs.c
+++ b/src/backend/nodes/outfuncs.c
@@ -378,6 +378,7 @@ _outModifyTable(StringInfo str, const ModifyTable *node)
 	WRITE_UINT_FIELD(rootRelation);
 	WRITE_BOOL_FIELD(partColsUpdated);
 	WRITE_NODE_FIELD(resultRelations);
+	WRITE_INT_FIELD(mergeTargetRelation);
 	WRITE_INT_FIELD(resultRelIndex);
 	WRITE_INT_FIELD(rootResultRelIndex);
 	WRITE_NODE_FIELD(plans);
@@ -393,6 +394,22 @@ _outModifyTable(StringInfo str, const ModifyTable *node)
 	WRITE_NODE_FIELD(onConflictWhere);
 	WRITE_UINT_FIELD(exclRelRTI);
 	WRITE_NODE_FIELD(exclRelTlist);
+	WRITE_NODE_FIELD(mergeSourceTargetList);
+	WRITE_NODE_FIELD(mergeActionList);
+}
+
+static void
+_outMergeWhenClause(StringInfo str, const MergeWhenClause *node)
+{
+	WRITE_NODE_TYPE("MERGEWHENCLAUSE");
+
+	WRITE_BOOL_FIELD(matched);
+	WRITE_ENUM_FIELD(commandType, CmdType);
+	WRITE_NODE_FIELD(condition);
+	WRITE_NODE_FIELD(targetList);
+	WRITE_NODE_FIELD(cols);
+	WRITE_NODE_FIELD(values);
+	WRITE_ENUM_FIELD(override, OverridingKind);
 }
 
 static void
@@ -1773,6 +1790,17 @@ _outOnConflictExpr(StringInfo str, const OnConflictExpr *node)
 	WRITE_NODE_FIELD(exclRelTlist);
 }
 
+static void
+_outMergeAction(StringInfo str, const MergeAction *node)
+{
+	WRITE_NODE_TYPE("MERGEACTION");
+
+	WRITE_BOOL_FIELD(matched);
+	WRITE_ENUM_FIELD(commandType, CmdType);
+	WRITE_NODE_FIELD(qual);
+	WRITE_NODE_FIELD(targetList);
+}
+
 /*****************************************************************************
  *
  *	Stuff from relation.h.
@@ -2179,6 +2207,7 @@ _outModifyTablePath(StringInfo str, const ModifyTablePath *node)
 	WRITE_UINT_FIELD(rootRelation);
 	WRITE_BOOL_FIELD(partColsUpdated);
 	WRITE_NODE_FIELD(resultRelations);
+	WRITE_INT_FIELD(mergeTargetRelation);
 	WRITE_NODE_FIELD(subpaths);
 	WRITE_NODE_FIELD(subroots);
 	WRITE_NODE_FIELD(withCheckOptionLists);
@@ -2186,6 +2215,8 @@ _outModifyTablePath(StringInfo str, const ModifyTablePath *node)
 	WRITE_NODE_FIELD(rowMarks);
 	WRITE_NODE_FIELD(onconflict);
 	WRITE_INT_FIELD(epqParam);
+	WRITE_NODE_FIELD(mergeSourceTargetList);
+	WRITE_NODE_FIELD(mergeActionList);
 }
 
 static void
@@ -2999,6 +3030,9 @@ _outQuery(StringInfo str, const Query *node)
 	WRITE_NODE_FIELD(setOperations);
 	WRITE_NODE_FIELD(constraintDeps);
 	WRITE_NODE_FIELD(withCheckOptions);
+	WRITE_INT_FIELD(mergeTarget_relation);
+	WRITE_NODE_FIELD(mergeSourceTargetList);
+	WRITE_NODE_FIELD(mergeActionList);
 	WRITE_LOCATION_FIELD(stmt_location);
 	WRITE_LOCATION_FIELD(stmt_len);
 }
@@ -3733,6 +3767,9 @@ outNode(StringInfo str, const void *obj)
 			case T_ModifyTable:
 				_outModifyTable(str, obj);
 				break;
+			case T_MergeWhenClause:
+				_outMergeWhenClause(str, obj);
+				break;
 			case T_Append:
 				_outAppend(str, obj);
 				break;
@@ -4021,6 +4058,9 @@ outNode(StringInfo str, const void *obj)
 			case T_OnConflictExpr:
 				_outOnConflictExpr(str, obj);
 				break;
+			case T_MergeAction:
+				_outMergeAction(str, obj);
+				break;
 			case T_Path:
 				_outPath(str, obj);
 				break;
diff --git a/src/backend/nodes/readfuncs.c b/src/backend/nodes/readfuncs.c
index e117867de5..4f7d088703 100644
--- a/src/backend/nodes/readfuncs.c
+++ b/src/backend/nodes/readfuncs.c
@@ -281,6 +281,9 @@ _readQuery(void)
 	READ_NODE_FIELD(setOperations);
 	READ_NODE_FIELD(constraintDeps);
 	READ_NODE_FIELD(withCheckOptions);
+	READ_INT_FIELD(mergeTarget_relation);
+	READ_NODE_FIELD(mergeSourceTargetList);
+	READ_NODE_FIELD(mergeActionList);
 	READ_LOCATION_FIELD(stmt_location);
 	READ_LOCATION_FIELD(stmt_len);
 
@@ -1339,6 +1342,22 @@ _readOnConflictExpr(void)
 	READ_DONE();
 }
 
+/*
+ * _readMergeAction
+ */
+static MergeAction *
+_readMergeAction(void)
+{
+	READ_LOCALS(MergeAction);
+
+	READ_BOOL_FIELD(matched);
+	READ_ENUM_FIELD(commandType, CmdType);
+	READ_NODE_FIELD(qual);
+	READ_NODE_FIELD(targetList);
+
+	READ_DONE();
+}
+
 /*
  *	Stuff from parsenodes.h.
  */
@@ -1600,6 +1619,7 @@ _readModifyTable(void)
 	READ_UINT_FIELD(rootRelation);
 	READ_BOOL_FIELD(partColsUpdated);
 	READ_NODE_FIELD(resultRelations);
+	READ_INT_FIELD(mergeTargetRelation);
 	READ_INT_FIELD(resultRelIndex);
 	READ_INT_FIELD(rootResultRelIndex);
 	READ_NODE_FIELD(plans);
@@ -1615,6 +1635,27 @@ _readModifyTable(void)
 	READ_NODE_FIELD(onConflictWhere);
 	READ_UINT_FIELD(exclRelRTI);
 	READ_NODE_FIELD(exclRelTlist);
+	READ_NODE_FIELD(mergeSourceTargetList);
+	READ_NODE_FIELD(mergeActionList);
+
+	READ_DONE();
+}
+
+/*
+ * _readMergeWhenClause
+ */
+static MergeWhenClause *
+_readMergeWhenClause(void)
+{
+	READ_LOCALS(MergeWhenClause);
+
+	READ_BOOL_FIELD(matched);
+	READ_ENUM_FIELD(commandType, CmdType);
+	READ_NODE_FIELD(condition);
+	READ_NODE_FIELD(targetList);
+	READ_NODE_FIELD(cols);
+	READ_NODE_FIELD(values);
+	READ_ENUM_FIELD(override, OverridingKind);
 
 	READ_DONE();
 }
@@ -2668,6 +2709,8 @@ parseNodeString(void)
 		return_value = _readFromExpr();
 	else if (MATCH("ONCONFLICTEXPR", 14))
 		return_value = _readOnConflictExpr();
+	else if (MATCH("MERGEACTION", 11))
+		return_value = _readMergeAction();
 	else if (MATCH("RTE", 3))
 		return_value = _readRangeTblEntry();
 	else if (MATCH("RANGETBLFUNCTION", 16))
@@ -2690,6 +2733,8 @@ parseNodeString(void)
 		return_value = _readProjectSet();
 	else if (MATCH("MODIFYTABLE", 11))
 		return_value = _readModifyTable();
+	else if (MATCH("MERGEWHENCLAUSE", 15))
+		return_value = _readMergeWhenClause();
 	else if (MATCH("APPEND", 6))
 		return_value = _readAppend();
 	else if (MATCH("MERGEAPPEND", 11))
diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index da7a92081a..87b2ee7cc7 100644
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -280,9 +280,12 @@ static ModifyTable *make_modifytable(PlannerInfo *root,
 				 CmdType operation, bool canSetTag,
 				 Index nominalRelation, Index rootRelation,
 				 bool partColsUpdated,
-				 List *resultRelations, List *subplans, List *subroots,
+				 List *resultRelations, Index mergeTargetRelation,
+				 List *subplans, List *subroots,
 				 List *withCheckOptionLists, List *returningLists,
-				 List *rowMarks, OnConflictExpr *onconflict, int epqParam);
+				 List *rowMarks, OnConflictExpr *onconflict,
+				 List *mergeSourceTargetList,
+				 List *mergeActionList, int epqParam);
 static GatherMerge *create_gather_merge_plan(PlannerInfo *root,
 						 GatherMergePath *best_path);
 
@@ -2409,12 +2412,15 @@ create_modifytable_plan(PlannerInfo *root, ModifyTablePath *best_path)
 							best_path->rootRelation,
 							best_path->partColsUpdated,
 							best_path->resultRelations,
+							best_path->mergeTargetRelation,
 							subplans,
 							best_path->subroots,
 							best_path->withCheckOptionLists,
 							best_path->returningLists,
 							best_path->rowMarks,
 							best_path->onconflict,
+							best_path->mergeSourceTargetList,
+							best_path->mergeActionList,
 							best_path->epqParam);
 
 	copy_generic_path_info(&plan->plan, &best_path->path);
@@ -6483,9 +6489,12 @@ make_modifytable(PlannerInfo *root,
 				 CmdType operation, bool canSetTag,
 				 Index nominalRelation, Index rootRelation,
 				 bool partColsUpdated,
-				 List *resultRelations, List *subplans, List *subroots,
+				 List *resultRelations, Index mergeTargetRelation,
+				 List *subplans, List *subroots,
 				 List *withCheckOptionLists, List *returningLists,
-				 List *rowMarks, OnConflictExpr *onconflict, int epqParam)
+				 List *rowMarks, OnConflictExpr *onconflict,
+				 List *mergeSourceTargetList,
+				 List *mergeActionList, int epqParam)
 {
 	ModifyTable *node = makeNode(ModifyTable);
 	List	   *fdw_private_list;
@@ -6513,6 +6522,7 @@ make_modifytable(PlannerInfo *root,
 	node->rootRelation = rootRelation;
 	node->partColsUpdated = partColsUpdated;
 	node->resultRelations = resultRelations;
+	node->mergeTargetRelation = mergeTargetRelation;
 	node->resultRelIndex = -1;	/* will be set correctly in setrefs.c */
 	node->rootResultRelIndex = -1;	/* will be set correctly in setrefs.c */
 	node->plans = subplans;
@@ -6545,6 +6555,8 @@ make_modifytable(PlannerInfo *root,
 	node->withCheckOptionLists = withCheckOptionLists;
 	node->returningLists = returningLists;
 	node->rowMarks = rowMarks;
+	node->mergeSourceTargetList = mergeSourceTargetList;
+	node->mergeActionList = mergeActionList;
 	node->epqParam = epqParam;
 
 	/*
diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
index c729a99f8b..9c06ece155 100644
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -801,6 +801,24 @@ subquery_planner(PlannerGlobal *glob, Query *parse,
 		/* exclRelTlist contains only Vars, so no preprocessing needed */
 	}
 
+	foreach(l, parse->mergeActionList)
+	{
+		MergeAction *action = (MergeAction *) lfirst(l);
+
+		action->targetList = (List *)
+			preprocess_expression(root,
+								  (Node *) action->targetList,
+								  EXPRKIND_TARGET);
+		action->qual =
+			preprocess_expression(root,
+								  (Node *) action->qual,
+								  EXPRKIND_QUAL);
+	}
+
+	parse->mergeSourceTargetList = (List *)
+		preprocess_expression(root, (Node *) parse->mergeSourceTargetList,
+							  EXPRKIND_TARGET);
+
 	root->append_rel_list = (List *)
 		preprocess_expression(root, (Node *) root->append_rel_list,
 							  EXPRKIND_APPINFO);
@@ -1548,6 +1566,7 @@ inheritance_planner(PlannerInfo *root)
 									 subroot->parse->returningList);
 
 		Assert(!parse->onConflict);
+		Assert(parse->mergeActionList == NIL);
 	}
 
 	/* Result path must go into outer query's FINAL upperrel */
@@ -1608,12 +1627,15 @@ inheritance_planner(PlannerInfo *root)
 									 rootRelation,
 									 root->partColsUpdated,
 									 resultRelations,
+									 0,
 									 subpaths,
 									 subroots,
 									 withCheckOptionLists,
 									 returningLists,
 									 rowMarks,
 									 NULL,
+									 NULL,
+									 NULL,
 									 SS_assign_special_param(root)));
 }
 
@@ -2144,8 +2166,8 @@ grouping_planner(PlannerInfo *root, bool inheritance_update,
 		}
 
 		/*
-		 * If this is an INSERT/UPDATE/DELETE, and we're not being called from
-		 * inheritance_planner, add the ModifyTable node.
+		 * If this is an INSERT/UPDATE/DELETE/MERGE, and we're not being
+		 * called from inheritance_planner, add the ModifyTable node.
 		 */
 		if (parse->commandType != CMD_SELECT && !inheritance_update)
 		{
@@ -2196,12 +2218,15 @@ grouping_planner(PlannerInfo *root, bool inheritance_update,
 										rootRelation,
 										false,
 										list_make1_int(parse->resultRelation),
+										parse->mergeTarget_relation,
 										list_make1(path),
 										list_make1(root),
 										withCheckOptionLists,
 										returningLists,
 										rowMarks,
 										parse->onConflict,
+										parse->mergeSourceTargetList,
+										parse->mergeActionList,
 										SS_assign_special_param(root));
 		}
 
diff --git a/src/backend/optimizer/plan/setrefs.c b/src/backend/optimizer/plan/setrefs.c
index 6d6ef1c376..734d7f7a7a 100644
--- a/src/backend/optimizer/plan/setrefs.c
+++ b/src/backend/optimizer/plan/setrefs.c
@@ -847,6 +847,60 @@ set_plan_refs(PlannerInfo *root, Plan *plan, int rtoffset)
 						fix_scan_list(root, splan->exclRelTlist, rtoffset);
 				}
 
+				/*
+				 * The MERGE statement produces the target rows by performing a
+				 * right join between the target relation and the source
+				 * relation (which could be a plain relation or a subquery).
+				 * The INSERT and UPDATE actions of the MERGE statement
+				 * requires access to the columns from the source relation. We
+				 * arrange things so that the source relation attributes are
+				 * available as INNER_VAR and the target relation attributes
+				 * are available from the scan tuple.
+				 */
+				if (splan->mergeActionList != NIL)
+				{
+					/*
+					 * mergeSourceTargetList is already setup correctly to
+					 * include all Vars coming from the source relation. So we
+					 * fix the targetList of individual action nodes by
+					 * ensuring that the source relation Vars are referenced
+					 * as INNER_VAR. Note that for this to work correctly,
+					 * during execution, the ecxt_innertuple must be set to
+					 * the tuple obtained from the source relation.
+					 *
+					 * We leave the Vars from the result relation (i.e. the
+					 * target relation) unchanged i.e. those Vars would be
+					 * picked from the scan slot. So during execution, we must
+					 * ensure that ecxt_scantuple is setup correctly to refer
+					 * to the tuple from the target relation.
+					 */
+
+					indexed_tlist *itlist;
+
+					itlist = build_tlist_index(splan->mergeSourceTargetList);
+
+					splan->mergeTargetRelation += rtoffset;
+
+					foreach(l, splan->mergeActionList)
+					{
+						MergeAction *action = (MergeAction *) lfirst(l);
+
+						/* Fix targetList of each action. */
+						action->targetList = fix_join_expr(root,
+								action->targetList,
+								NULL, itlist,
+								linitial_int(splan->resultRelations),
+								rtoffset);
+
+						/* Fix quals too. */
+						action->qual = (Node *) fix_join_expr(root,
+								(List *) action->qual,
+								NULL, itlist,
+								linitial_int(splan->resultRelations),
+								rtoffset);
+					}
+				}
+
 				splan->nominalRelation += rtoffset;
 				if (splan->rootRelation)
 					splan->rootRelation += rtoffset;
diff --git a/src/backend/optimizer/prep/preptlist.c b/src/backend/optimizer/prep/preptlist.c
index 8603feef2b..8a87cfd14a 100644
--- a/src/backend/optimizer/prep/preptlist.c
+++ b/src/backend/optimizer/prep/preptlist.c
@@ -118,6 +118,46 @@ preprocess_targetlist(PlannerInfo *root)
 		tlist = expand_targetlist(tlist, command_type,
 								  result_relation, target_relation);
 
+	if (command_type == CMD_MERGE)
+	{
+		ListCell   *l;
+
+		/*
+		 * For MERGE, add any junk column(s) needed to allow the executor to
+		 * identify the rows to be updated or deleted, with different
+		 * handling for partitioned tables.
+		 */
+		rewriteTargetListMerge(parse, target_relation);
+
+		/*
+		 * For MERGE command, handle targetlist of each MergeAction separately.
+		 * Give the same treatment to MergeAction->targetList as we would have
+		 * given to a regular INSERT/UPDATE/DELETE.
+		 */
+		foreach(l, parse->mergeActionList)
+		{
+			MergeAction *action = (MergeAction *) lfirst(l);
+
+			switch (action->commandType)
+			{
+				case CMD_INSERT:
+				case CMD_UPDATE:
+					action->targetList = expand_targetlist(action->targetList,
+														   action->commandType,
+														   result_relation,
+														   target_relation);
+					break;
+				case CMD_DELETE:
+					break;
+				case CMD_NOTHING:
+					break;
+				default:
+					elog(ERROR, "unknown action in MERGE WHEN clause");
+
+			}
+		}
+	}
+
 	/*
 	 * Add necessary junk columns for rowmarked rels.  These values are needed
 	 * for locking of rels selected FOR UPDATE/SHARE, and to do EvalPlanQual
@@ -348,6 +388,7 @@ expand_targetlist(List *tlist, int command_type,
 													  true /* byval */ );
 					}
 					break;
+				case CMD_MERGE:
 				case CMD_UPDATE:
 					if (!att_tup->attisdropped)
 					{
diff --git a/src/backend/optimizer/util/pathnode.c b/src/backend/optimizer/util/pathnode.c
index d50d86b252..f699cb0e72 100644
--- a/src/backend/optimizer/util/pathnode.c
+++ b/src/backend/optimizer/util/pathnode.c
@@ -3303,17 +3303,21 @@ create_lockrows_path(PlannerInfo *root, RelOptInfo *rel,
  * 'rowMarks' is a list of PlanRowMarks (non-locking only)
  * 'onconflict' is the ON CONFLICT clause, or NULL
  * 'epqParam' is the ID of Param for EvalPlanQual re-eval
+ * 'mergeActionList' is a list of MERGE actions
  */
 ModifyTablePath *
 create_modifytable_path(PlannerInfo *root, RelOptInfo *rel,
 						CmdType operation, bool canSetTag,
 						Index nominalRelation, Index rootRelation,
 						bool partColsUpdated,
-						List *resultRelations, List *subpaths,
+						List *resultRelations,
+						Index mergeTargetRelation,
+						List *subpaths,
 						List *subroots,
 						List *withCheckOptionLists, List *returningLists,
 						List *rowMarks, OnConflictExpr *onconflict,
-						int epqParam)
+						List *mergeSourceTargetList,
+						List *mergeActionList, int epqParam)
 {
 	ModifyTablePath *pathnode = makeNode(ModifyTablePath);
 	double		total_size;
@@ -3378,6 +3382,7 @@ create_modifytable_path(PlannerInfo *root, RelOptInfo *rel,
 	pathnode->rootRelation = rootRelation;
 	pathnode->partColsUpdated = partColsUpdated;
 	pathnode->resultRelations = resultRelations;
+	pathnode->mergeTargetRelation = mergeTargetRelation;
 	pathnode->subpaths = subpaths;
 	pathnode->subroots = subroots;
 	pathnode->withCheckOptionLists = withCheckOptionLists;
@@ -3385,6 +3390,8 @@ create_modifytable_path(PlannerInfo *root, RelOptInfo *rel,
 	pathnode->rowMarks = rowMarks;
 	pathnode->onconflict = onconflict;
 	pathnode->epqParam = epqParam;
+	pathnode->mergeSourceTargetList = mergeSourceTargetList;
+	pathnode->mergeActionList = mergeActionList;
 
 	return pathnode;
 }
diff --git a/src/backend/optimizer/util/plancat.c b/src/backend/optimizer/util/plancat.c
index a570ac0aab..79d57f93eb 100644
--- a/src/backend/optimizer/util/plancat.c
+++ b/src/backend/optimizer/util/plancat.c
@@ -1880,6 +1880,10 @@ has_row_triggers(PlannerInfo *root, Index rti, CmdType event)
 				 trigDesc->trig_delete_before_row))
 				result = true;
 			break;
+			/* There is no separate event for MERGE, only INSERT/UPDATE/DELETE */
+		case CMD_MERGE:
+			result = false;
+			break;
 		default:
 			elog(ERROR, "unrecognized CmdType: %d", (int) event);
 			break;
diff --git a/src/backend/parser/Makefile b/src/backend/parser/Makefile
index f14febdbda..95fdf0b973 100644
--- a/src/backend/parser/Makefile
+++ b/src/backend/parser/Makefile
@@ -14,7 +14,7 @@ override CPPFLAGS := -I. -I$(srcdir) $(CPPFLAGS)
 
 OBJS= analyze.o gram.o scan.o parser.o \
       parse_agg.o parse_clause.o parse_coerce.o parse_collate.o parse_cte.o \
-      parse_enr.o parse_expr.o parse_func.o parse_node.o parse_oper.o \
+      parse_enr.o parse_expr.o parse_func.o parse_merge.o parse_node.o parse_oper.o \
       parse_param.o parse_relation.o parse_target.o parse_type.o \
       parse_utilcmd.o scansup.o
 
diff --git a/src/backend/parser/analyze.c b/src/backend/parser/analyze.c
index 226927b7ab..b8c79d32c1 100644
--- a/src/backend/parser/analyze.c
+++ b/src/backend/parser/analyze.c
@@ -38,6 +38,7 @@
 #include "parser/parse_cte.h"
 #include "parser/parse_expr.h"
 #include "parser/parse_func.h"
+#include "parser/parse_merge.h"
 #include "parser/parse_oper.h"
 #include "parser/parse_param.h"
 #include "parser/parse_relation.h"
@@ -53,9 +54,6 @@ post_parse_analyze_hook_type post_parse_analyze_hook = NULL;
 static Query *transformOptionalSelectInto(ParseState *pstate, Node *parseTree);
 static Query *transformDeleteStmt(ParseState *pstate, DeleteStmt *stmt);
 static Query *transformInsertStmt(ParseState *pstate, InsertStmt *stmt);
-static List *transformInsertRow(ParseState *pstate, List *exprlist,
-				   List *stmtcols, List *icolumns, List *attrnos,
-				   bool strip_indirection);
 static OnConflictExpr *transformOnConflictClause(ParseState *pstate,
 						  OnConflictClause *onConflictClause);
 static int	count_rowexpr_columns(ParseState *pstate, Node *expr);
@@ -68,8 +66,6 @@ static void determineRecursiveColTypes(ParseState *pstate,
 						   Node *larg, List *nrtargetlist);
 static Query *transformUpdateStmt(ParseState *pstate, UpdateStmt *stmt);
 static List *transformReturningList(ParseState *pstate, List *returningList);
-static List *transformUpdateTargetList(ParseState *pstate,
-						  List *targetList);
 static Query *transformDeclareCursorStmt(ParseState *pstate,
 						   DeclareCursorStmt *stmt);
 static Query *transformExplainStmt(ParseState *pstate,
@@ -267,6 +263,7 @@ transformStmt(ParseState *pstate, Node *parseTree)
 		case T_InsertStmt:
 		case T_UpdateStmt:
 		case T_DeleteStmt:
+		case T_MergeStmt:
 			(void) test_raw_expression_coverage(parseTree, NULL);
 			break;
 		default:
@@ -291,6 +288,10 @@ transformStmt(ParseState *pstate, Node *parseTree)
 			result = transformUpdateStmt(pstate, (UpdateStmt *) parseTree);
 			break;
 
+		case T_MergeStmt:
+			result = transformMergeStmt(pstate, (MergeStmt *) parseTree);
+			break;
+
 		case T_SelectStmt:
 			{
 				SelectStmt *n = (SelectStmt *) parseTree;
@@ -366,6 +367,7 @@ analyze_requires_snapshot(RawStmt *parseTree)
 		case T_InsertStmt:
 		case T_DeleteStmt:
 		case T_UpdateStmt:
+		case T_MergeStmt:
 		case T_SelectStmt:
 			result = true;
 			break;
@@ -896,7 +898,7 @@ transformInsertStmt(ParseState *pstate, InsertStmt *stmt)
  * attrnos: integer column numbers (must be same length as icolumns)
  * strip_indirection: if true, remove any field/array assignment nodes
  */
-static List *
+List *
 transformInsertRow(ParseState *pstate, List *exprlist,
 				   List *stmtcols, List *icolumns, List *attrnos,
 				   bool strip_indirection)
@@ -2287,9 +2289,9 @@ transformUpdateStmt(ParseState *pstate, UpdateStmt *stmt)
 
 /*
  * transformUpdateTargetList -
- *	handle SET clause in UPDATE/INSERT ... ON CONFLICT UPDATE
+ *	handle SET clause in UPDATE/MERGE/INSERT ... ON CONFLICT UPDATE
  */
-static List *
+List *
 transformUpdateTargetList(ParseState *pstate, List *origTlist)
 {
 	List	   *tlist = NIL;
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index 2c2208ffb7..3b48e1f507 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -241,6 +241,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 	PartitionSpec		*partspec;
 	PartitionBoundSpec	*partboundspec;
 	RoleSpec			*rolespec;
+	MergeWhenClause		*mergewhen;
 }
 
 %type <node>	stmt schema_stmt
@@ -282,6 +283,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 		CreateMatViewStmt RefreshMatViewStmt CreateAmStmt
 		CreatePublicationStmt AlterPublicationStmt
 		CreateSubscriptionStmt AlterSubscriptionStmt DropSubscriptionStmt
+		MergeStmt
 
 %type <node>	select_no_parens select_with_parens select_clause
 				simple_select values_clause
@@ -400,6 +402,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 				TriggerTransitions TriggerReferencing
 				publication_name_list
 				vacuum_relation_list opt_vacuum_relation_list
+				merge_values_clause
 
 %type <list>	group_by_list
 %type <node>	group_by_item empty_grouping_set rollup_clause cube_clause
@@ -460,6 +463,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 %type <istmt>	insert_rest
 %type <infer>	opt_conf_expr
 %type <onconflict> opt_on_conflict
+%type <mergewhen>	merge_insert merge_update merge_delete
 
 %type <vsetstmt> generic_set set_rest set_rest_more generic_reset reset_rest
 				 SetResetClause FunctionSetResetClause
@@ -585,6 +589,9 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 %type <list>		hash_partbound partbound_datum_list range_datum_list
 %type <defelt>		hash_partbound_elem
 
+%type <node>	merge_when_clause opt_merge_when_and_condition
+%type <list>	merge_when_list
+
 /*
  * Non-keyword token types.  These are hard-wired into the "flex" lexer.
  * They must be listed first so that their numeric codes do not depend on
@@ -652,7 +659,8 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 	LEADING LEAKPROOF LEAST LEFT LEVEL LIKE LIMIT LISTEN LOAD LOCAL
 	LOCALTIME LOCALTIMESTAMP LOCATION LOCK_P LOCKED LOGGED
 
-	MAPPING MATCH MATERIALIZED MAXVALUE METHOD MINUTE_P MINVALUE MODE MONTH_P MOVE
+	MAPPING MATCH MATCHED MATERIALIZED MAXVALUE MERGE METHOD
+	MINUTE_P MINVALUE MODE MONTH_P MOVE
 
 	NAME_P NAMES NATIONAL NATURAL NCHAR NEW NEXT NO NONE
 	NOT NOTHING NOTIFY NOTNULL NOWAIT NULL_P NULLIF
@@ -920,6 +928,7 @@ stmt :
 			| RefreshMatViewStmt
 			| LoadStmt
 			| LockStmt
+			| MergeStmt
 			| NotifyStmt
 			| PrepareStmt
 			| ReassignOwnedStmt
@@ -10655,6 +10664,7 @@ ExplainableStmt:
 			| InsertStmt
 			| UpdateStmt
 			| DeleteStmt
+			| MergeStmt
 			| DeclareCursorStmt
 			| CreateAsStmt
 			| CreateMatViewStmt
@@ -10717,6 +10727,7 @@ PreparableStmt:
 			| InsertStmt
 			| UpdateStmt
 			| DeleteStmt					/* by default all are $$=$1 */
+			| MergeStmt
 		;
 
 /*****************************************************************************
@@ -11083,6 +11094,142 @@ set_target_list:
 		;
 
 
+/*****************************************************************************
+ *
+ *		QUERY:
+ *				MERGE STATEMENTS
+ *
+ *****************************************************************************/
+
+MergeStmt:
+			opt_with_clause MERGE INTO relation_expr_opt_alias
+			USING table_ref
+			ON a_expr
+			merge_when_list
+				{
+					MergeStmt *m = makeNode(MergeStmt);
+
+					m->withClause = $1;
+					m->relation = $4;
+					m->source_relation = $6;
+					m->join_condition = $8;
+					m->mergeWhenClauses = $9;
+
+					$$ = (Node *)m;
+				}
+			;
+
+
+merge_when_list:
+			merge_when_clause						{ $$ = list_make1($1); }
+			| merge_when_list merge_when_clause		{ $$ = lappend($1,$2); }
+			;
+
+merge_when_clause:
+			WHEN MATCHED opt_merge_when_and_condition THEN merge_update
+				{
+					$5->matched = true;
+					$5->commandType = CMD_UPDATE;
+					$5->condition = $3;
+
+					$$ = (Node *) $5;
+				}
+			| WHEN MATCHED opt_merge_when_and_condition THEN merge_delete
+				{
+					MergeWhenClause *m = makeNode(MergeWhenClause);
+
+					m->matched = true;
+					m->commandType = CMD_DELETE;
+					m->condition = $3;
+
+					$$ = (Node *)m;
+				}
+			| WHEN NOT MATCHED opt_merge_when_and_condition THEN merge_insert
+				{
+					$6->matched = false;
+					$6->commandType = CMD_INSERT;
+					$6->condition = $4;
+
+					$$ = (Node *) $6;
+				}
+			| WHEN NOT MATCHED opt_merge_when_and_condition THEN DO NOTHING
+				{
+					MergeWhenClause *m = makeNode(MergeWhenClause);
+
+					m->matched = false;
+					m->commandType = CMD_NOTHING;
+					m->condition = $4;
+
+					$$ = (Node *)m;
+				}
+			;
+
+opt_merge_when_and_condition:
+			AND a_expr 				{ $$ = $2; }
+			| 			 			{ $$ = NULL; }
+			;
+
+merge_delete:
+			DELETE_P 				{ $$ = NULL; }
+			;
+
+merge_update:
+			UPDATE SET set_clause_list
+				{
+					MergeWhenClause *n = makeNode(MergeWhenClause);
+					n->targetList = $3;
+
+					$$ = n;
+				}
+			;
+
+merge_insert:
+			INSERT merge_values_clause
+				{
+					MergeWhenClause *n = makeNode(MergeWhenClause);
+					n->cols = NIL;
+					n->values = $2;
+					$$ = n;
+				}
+			| INSERT OVERRIDING override_kind VALUE_P merge_values_clause
+				{
+					MergeWhenClause *n = makeNode(MergeWhenClause);
+					n->cols = NIL;
+					n->override = $3;
+					n->values = $5;
+					$$ = n;
+				}
+			| INSERT '(' insert_column_list ')' merge_values_clause
+				{
+					MergeWhenClause *n = makeNode(MergeWhenClause);
+					n->cols = $3;
+					n->values = $5;
+					$$ = n;
+				}
+			| INSERT '(' insert_column_list ')' OVERRIDING override_kind VALUE_P merge_values_clause
+				{
+					MergeWhenClause *n = makeNode(MergeWhenClause);
+					n->cols = $3;
+					n->override = $6;
+					n->values = $8;
+					$$ = n;
+				}
+			| INSERT DEFAULT VALUES
+				{
+					MergeWhenClause *n = makeNode(MergeWhenClause);
+					n->cols = NIL;
+					n->values = NIL;
+					$$ = n;
+				}
+			;
+
+merge_values_clause:
+			VALUES '(' expr_list ')'
+				{
+					$$ = $3;
+				}
+			;
+
 /*****************************************************************************
  *
  *		QUERY:
@@ -15103,8 +15250,10 @@ unreserved_keyword:
 			| LOGGED
 			| MAPPING
 			| MATCH
+			| MATCHED
 			| MATERIALIZED
 			| MAXVALUE
+			| MERGE
 			| METHOD
 			| MINUTE_P
 			| MINVALUE
diff --git a/src/backend/parser/parse_agg.c b/src/backend/parser/parse_agg.c
index 61727e1d71..0307738946 100644
--- a/src/backend/parser/parse_agg.c
+++ b/src/backend/parser/parse_agg.c
@@ -455,6 +455,13 @@ check_agglevels_and_constraints(ParseState *pstate, Node *expr)
 		case EXPR_KIND_VALUES_SINGLE:
 			errkind = true;
 			break;
+		case EXPR_KIND_MERGE_WHEN_AND:
+			if (isAgg)
+				err = _("aggregate functions are not allowed in WHEN AND conditions");
+			else
+				err = _("grouping operations are not allowed in WHEN AND conditions");
+
+			break;
 		case EXPR_KIND_CHECK_CONSTRAINT:
 		case EXPR_KIND_DOMAIN_CHECK:
 			if (isAgg)
@@ -873,6 +880,9 @@ transformWindowFuncCall(ParseState *pstate, WindowFunc *wfunc,
 		case EXPR_KIND_VALUES_SINGLE:
 			errkind = true;
 			break;
+		case EXPR_KIND_MERGE_WHEN_AND:
+			err = _("window functions are not allowed in WHEN AND conditions");
+			break;
 		case EXPR_KIND_CHECK_CONSTRAINT:
 		case EXPR_KIND_DOMAIN_CHECK:
 			err = _("window functions are not allowed in check constraints");
diff --git a/src/backend/parser/parse_clause.c b/src/backend/parser/parse_clause.c
index 4ba51203a6..45d2115ce6 100644
--- a/src/backend/parser/parse_clause.c
+++ b/src/backend/parser/parse_clause.c
@@ -76,9 +76,6 @@ static RangeTblEntry *transformRangeTableFunc(ParseState *pstate,
 						RangeTableFunc *t);
 static TableSampleClause *transformRangeTableSample(ParseState *pstate,
 						  RangeTableSample *rts);
-static Node *transformFromClauseItem(ParseState *pstate, Node *n,
-						RangeTblEntry **top_rte, int *top_rti,
-						List **namespace);
 static Node *buildMergedJoinVar(ParseState *pstate, JoinType jointype,
 				   Var *l_colvar, Var *r_colvar);
 static ParseNamespaceItem *makeNamespaceItem(RangeTblEntry *rte,
@@ -139,6 +136,7 @@ transformFromClause(ParseState *pstate, List *frmList)
 		n = transformFromClauseItem(pstate, n,
 									&rte,
 									&rtindex,
+									NULL, NULL,
 									&namespace);
 
 		checkNameSpaceConflicts(pstate, pstate->p_namespace, namespace);
@@ -1058,14 +1056,21 @@ getRTEForSpecialRelationTypes(ParseState *pstate, RangeVar *rv)
  *
  * *top_rti: receives the rangetable index of top_rte.  (Ditto.)
  *
+ * *right_rte: receives the RTE corresponding to the right side of the
+ * jointree. Only MERGE really needs to know about this and only MERGE passes a
+ * non-NULL pointer.
+ *
+ * *right_rti: receives the rangetable index of the right_rte.
+ *
  * *namespace: receives a List of ParseNamespaceItems for the RTEs exposed
  * as table/column names by this item.  (The lateral_only flags in these items
  * are indeterminate and should be explicitly set by the caller before use.)
  */
-static Node *
+Node *
 transformFromClauseItem(ParseState *pstate, Node *n,
 						RangeTblEntry **top_rte, int *top_rti,
-						List **namespace)
+						RangeTblEntry **right_rte, int *right_rti,
+						List **fnamespace)
 {
 	if (IsA(n, RangeVar))
 	{
@@ -1087,7 +1092,7 @@ transformFromClauseItem(ParseState *pstate, Node *n,
 		Assert(rte == rt_fetch(rtindex, pstate->p_rtable));
 		*top_rte = rte;
 		*top_rti = rtindex;
-		*namespace = list_make1(makeDefaultNSItem(rte));
+		*fnamespace = list_make1(makeDefaultNSItem(rte));
 		rtr = makeNode(RangeTblRef);
 		rtr->rtindex = rtindex;
 		return (Node *) rtr;
@@ -1105,7 +1110,7 @@ transformFromClauseItem(ParseState *pstate, Node *n,
 		Assert(rte == rt_fetch(rtindex, pstate->p_rtable));
 		*top_rte = rte;
 		*top_rti = rtindex;
-		*namespace = list_make1(makeDefaultNSItem(rte));
+		*fnamespace = list_make1(makeDefaultNSItem(rte));
 		rtr = makeNode(RangeTblRef);
 		rtr->rtindex = rtindex;
 		return (Node *) rtr;
@@ -1123,7 +1128,7 @@ transformFromClauseItem(ParseState *pstate, Node *n,
 		Assert(rte == rt_fetch(rtindex, pstate->p_rtable));
 		*top_rte = rte;
 		*top_rti = rtindex;
-		*namespace = list_make1(makeDefaultNSItem(rte));
+		*fnamespace = list_make1(makeDefaultNSItem(rte));
 		rtr = makeNode(RangeTblRef);
 		rtr->rtindex = rtindex;
 		return (Node *) rtr;
@@ -1141,7 +1146,7 @@ transformFromClauseItem(ParseState *pstate, Node *n,
 		Assert(rte == rt_fetch(rtindex, pstate->p_rtable));
 		*top_rte = rte;
 		*top_rti = rtindex;
-		*namespace = list_make1(makeDefaultNSItem(rte));
+		*fnamespace = list_make1(makeDefaultNSItem(rte));
 		rtr = makeNode(RangeTblRef);
 		rtr->rtindex = rtindex;
 		return (Node *) rtr;
@@ -1156,7 +1161,7 @@ transformFromClauseItem(ParseState *pstate, Node *n,
 
 		/* Recursively transform the contained relation */
 		rel = transformFromClauseItem(pstate, rts->relation,
-									  top_rte, top_rti, namespace);
+									  top_rte, top_rti, NULL, NULL, fnamespace);
 		/* Currently, grammar could only return a RangeVar as contained rel */
 		rtr = castNode(RangeTblRef, rel);
 		rte = rt_fetch(rtr->rtindex, pstate->p_rtable);
@@ -1184,6 +1189,7 @@ transformFromClauseItem(ParseState *pstate, Node *n,
 		List	   *l_namespace,
 				   *r_namespace,
 				   *my_namespace,
+				   *save_namespace,
 				   *l_colnames,
 				   *r_colnames,
 				   *res_colnames,
@@ -1202,6 +1208,7 @@ transformFromClauseItem(ParseState *pstate, Node *n,
 		j->larg = transformFromClauseItem(pstate, j->larg,
 										  &l_rte,
 										  &l_rtindex,
+										  NULL, NULL,
 										  &l_namespace);
 
 		/*
@@ -1225,12 +1232,34 @@ transformFromClauseItem(ParseState *pstate, Node *n,
 		sv_namespace_length = list_length(pstate->p_namespace);
 		pstate->p_namespace = list_concat(pstate->p_namespace, l_namespace);
 
+		/*
+		 * If we are running MERGE, don't make the other RTEs visible while
+		 * parsing the source relation. It mustn't see them.
+		 *
+		 * Currently, only MERGE passes non-NULL value for right_rte, so we
+		 * can safely deduce if we're running MERGE or not by just looking at
+		 * the right_rte. If that ever changes, we should look at other means
+		 * to find that.
+		 */
+		if (right_rte)
+		{
+			save_namespace = pstate->p_namespace;
+			pstate->p_namespace = NIL;
+		}
+
 		/* And now we can process the RHS */
 		j->rarg = transformFromClauseItem(pstate, j->rarg,
 										  &r_rte,
 										  &r_rtindex,
+										  NULL, NULL,
 										  &r_namespace);
 
+		/*
+		 * And now restore the namespace again so that join-quals can see it.
+		 */
+		if (right_rte)
+			pstate->p_namespace = save_namespace;
+
 		/* Remove the left-side RTEs from the namespace list again */
 		pstate->p_namespace = list_truncate(pstate->p_namespace,
 											sv_namespace_length);
@@ -1257,6 +1286,12 @@ transformFromClauseItem(ParseState *pstate, Node *n,
 		expandRTE(r_rte, r_rtindex, 0, -1, false,
 				  &r_colnames, &r_colvars);
 
+		if (right_rte)
+			*right_rte = r_rte;
+
+		if (right_rti)
+			*right_rti = r_rtindex;
+
 		/*
 		 * Natural join does not explicitly specify columns; must generate
 		 * columns to join. Need to run through the list of columns from each
@@ -1485,7 +1520,7 @@ transformFromClauseItem(ParseState *pstate, Node *n,
 		 * The join RTE itself is always made visible for unqualified column
 		 * names.  It's visible as a relation name only if it has an alias.
 		 */
-		*namespace = lappend(my_namespace,
+		*fnamespace = lappend(my_namespace,
 							 makeNamespaceItem(rte,
 											   (j->alias != NULL),
 											   true,
diff --git a/src/backend/parser/parse_collate.c b/src/backend/parser/parse_collate.c
index 6d34245083..51c73c4018 100644
--- a/src/backend/parser/parse_collate.c
+++ b/src/backend/parser/parse_collate.c
@@ -485,6 +485,7 @@ assign_collations_walker(Node *node, assign_collations_context *context)
 		case T_FromExpr:
 		case T_OnConflictExpr:
 		case T_SortGroupClause:
+		case T_MergeAction:
 			(void) expression_tree_walker(node,
 										  assign_collations_walker,
 										  (void *) &loccontext);
diff --git a/src/backend/parser/parse_expr.c b/src/backend/parser/parse_expr.c
index 385e54a9b6..38fbe3366f 100644
--- a/src/backend/parser/parse_expr.c
+++ b/src/backend/parser/parse_expr.c
@@ -1818,6 +1818,7 @@ transformSubLink(ParseState *pstate, SubLink *sublink)
 		case EXPR_KIND_RETURNING:
 		case EXPR_KIND_VALUES:
 		case EXPR_KIND_VALUES_SINGLE:
+		case EXPR_KIND_MERGE_WHEN_AND:
 			/* okay */
 			break;
 		case EXPR_KIND_CHECK_CONSTRAINT:
@@ -3475,6 +3476,8 @@ ParseExprKindName(ParseExprKind exprKind)
 			return "PARTITION BY";
 		case EXPR_KIND_CALL_ARGUMENT:
 			return "CALL";
+		case EXPR_KIND_MERGE_WHEN_AND:
+			return "MERGE WHEN AND";
 
 			/*
 			 * There is intentionally no default: case here, so that the
diff --git a/src/backend/parser/parse_func.c b/src/backend/parser/parse_func.c
index 44257154b8..be2fc1d51c 100644
--- a/src/backend/parser/parse_func.c
+++ b/src/backend/parser/parse_func.c
@@ -2341,6 +2341,9 @@ check_srf_call_placement(ParseState *pstate, Node *last_srf, int location)
 			/* okay, since we process this like a SELECT tlist */
 			pstate->p_hasTargetSRFs = true;
 			break;
+		case EXPR_KIND_MERGE_WHEN_AND:
+			err = _("set-returning functions are not allowed in WHEN AND conditions");
+			break;
 		case EXPR_KIND_CHECK_CONSTRAINT:
 		case EXPR_KIND_DOMAIN_CHECK:
 			err = _("set-returning functions are not allowed in check constraints");
diff --git a/src/backend/parser/parse_merge.c b/src/backend/parser/parse_merge.c
new file mode 100644
index 0000000000..722cb23b86
--- /dev/null
+++ b/src/backend/parser/parse_merge.c
@@ -0,0 +1,654 @@
+/*-------------------------------------------------------------------------
+ *
+ * parse_merge.c
+ *	  handle merge-statement in parser
+ *
+ * Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/parser/parse_merge.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "miscadmin.h"
+
+#include "access/sysattr.h"
+#include "nodes/makefuncs.h"
+#include "parser/analyze.h"
+#include "parser/parse_collate.h"
+#include "parser/parsetree.h"
+#include "parser/parser.h"
+#include "parser/parse_clause.h"
+#include "parser/parse_cte.h"
+#include "parser/parse_merge.h"
+#include "parser/parse_relation.h"
+#include "parser/parse_target.h"
+#include "utils/rel.h"
+#include "utils/relcache.h"
+
+static int transformMergeJoinClause(ParseState *pstate, Node *merge,
+						List **mergeSourceTargetList);
+static void setNamespaceForMergeWhen(ParseState *pstate,
+						MergeWhenClause *mergeWhenClause);
+static void setNamespaceVisibilityForRTE(List *namespace, RangeTblEntry *rte,
+							 bool rel_visible,
+							 bool cols_visible);
+static List *expandSourceTL(ParseState *pstate, RangeTblEntry *rte,
+							int rtindex);
+
+/*
+ *	Special handling for MERGE statement is required because we assemble
+ *	the query manually. This is similar to setTargetTable() followed
+ * 	by transformFromClause() but with a few less steps.
+ *
+ *	Process the FROM clause and add items to the query's range table,
+ *	joinlist, and namespace.
+ *
+ *	A special targetlist comprising of the columns from the right-subtree of
+ *	the join is populated and returned. Note that when the JoinExpr is
+ *	setup by transformMergeStmt, the left subtree has the target result
+ *	relation and the right subtree has the source relation.
+ *
+ *	Returns the rangetable index of the target relation.
+ */
+static int
+transformMergeJoinClause(ParseState *pstate, Node *merge,
+						 List **mergeSourceTargetList)
+{
+	RangeTblEntry *rte,
+			   *rt_rte;
+	List	   *namespace;
+	int			rtindex,
+				rt_rtindex;
+	Node	   *n;
+	int			mergeTarget_relation = list_length(pstate->p_rtable) + 1;
+	Var		   *var;
+	TargetEntry *te;
+
+	n = transformFromClauseItem(pstate, merge,
+								&rte,
+								&rtindex,
+								&rt_rte,
+								&rt_rtindex,
+								&namespace);
+
+	pstate->p_joinlist = list_make1(n);
+
+	/*
+	 * We created an internal join between the target and the source relation
+	 * to carry out the MERGE actions. Normally such an unaliased join hides
+	 * the joining relations, unless the column references are qualified.
+	 * Also, any unqualified column references are resolved to the Join RTE, if
+	 * there is a matching entry in the targetlist. But the way MERGE
+	 * execution is later setup, we expect all column references to resolve to
+	 * either the source or the target relation. Hence we must not add the
+	 * Join RTE to the namespace.
+	 *
+	 * The last entry must be for the top-level Join RTE. We don't want to
+	 * resolve any references to the Join RTE. So discard that.
+	 *
+	 * We also do not want to resolve any references from the leftside of the
+	 * Join since that corresponds to the target relation. References to the
+	 * columns of the target relation must be resolved from the result
+	 * relation and not the one that is used in the join. So the
+	 * mergeTarget_relation is marked invisible to both qualified as well as
+	 * unqualified references.
+	 */
+	Assert(list_length(namespace) > 1);
+	namespace = list_truncate(namespace, list_length(namespace) - 1);
+	pstate->p_namespace = list_concat(pstate->p_namespace, namespace);
+
+	setNamespaceVisibilityForRTE(pstate->p_namespace,
+								 rt_fetch(mergeTarget_relation, pstate->p_rtable), false, false);
+
+	/*
+	 * Expand the right relation and add its columns to the
+	 * mergeSourceTargetList. Note that the right relation can either be a
+	 * plain relation or a subquery or anything that can have a
+	 * RangeTableEntry.
+	 */
+	*mergeSourceTargetList = expandSourceTL(pstate, rt_rte, rt_rtindex);
+
+	/*
+	 * Add a whole-row-Var entry to support references to "source.*".
+	 */
+	var = makeWholeRowVar(rt_rte, rt_rtindex, 0, false);
+	te = makeTargetEntry((Expr *) var, list_length(*mergeSourceTargetList) + 1,
+						 NULL, true);
+	*mergeSourceTargetList = lappend(*mergeSourceTargetList, te);
+
+	return mergeTarget_relation;
+}
+
+/*
+ * Make appropriate changes to the namespace visibility while transforming
+ * individual action's quals and targetlist expressions. In particular, for
+ * INSERT actions we must only see the source relation (since INSERT action is
+ * invoked for NOT MATCHED tuples and hence there is no target tuple to deal
+ * with). On the other hand, UPDATE and DELETE actions can see both source and
+ * target relations.
+ *
+ * Also, since the internal Join node can hide the source and target
+ * relations, we must explicitly make the respective relation as visible so
+ * that columns can be referenced unqualified from these relations.
+ */
+static void
+setNamespaceForMergeWhen(ParseState *pstate, MergeWhenClause *mergeWhenClause)
+{
+	RangeTblEntry *targetRelRTE,
+			   *sourceRelRTE;
+
+	/* Assume target relation is at index 1 */
+	targetRelRTE = rt_fetch(1, pstate->p_rtable);
+
+	/*
+	 * Assume that the top-level join RTE is at the end. The source relation
+	 * is just before that.
+	 */
+	sourceRelRTE = rt_fetch(list_length(pstate->p_rtable) - 1, pstate->p_rtable);
+
+	switch (mergeWhenClause->commandType)
+	{
+		case CMD_INSERT:
+
+			/*
+			 * Inserts can't see target relation, but they can see source
+			 * relation.
+			 */
+			setNamespaceVisibilityForRTE(pstate->p_namespace,
+										 targetRelRTE, false, false);
+			setNamespaceVisibilityForRTE(pstate->p_namespace,
+										 sourceRelRTE, true, true);
+			break;
+
+		case CMD_UPDATE:
+		case CMD_DELETE:
+
+			/*
+			 * Updates and deletes can see both target and source relations.
+			 */
+			setNamespaceVisibilityForRTE(pstate->p_namespace,
+										 targetRelRTE, true, true);
+			setNamespaceVisibilityForRTE(pstate->p_namespace,
+										 sourceRelRTE, true, true);
+			break;
+
+		case CMD_NOTHING:
+			break;
+		default:
+			elog(ERROR, "unknown action in MERGE WHEN clause");
+	}
+}
+
+/*
+ * transformMergeStmt -
+ *	  transforms a MERGE statement
+ */
+Query *
+transformMergeStmt(ParseState *pstate, MergeStmt *stmt)
+{
+	Query		   *qry = makeNode(Query);
+	ListCell	   *l;
+	AclMode			targetPerms = ACL_NO_RIGHTS;
+	bool			is_terminal[2];
+	JoinExpr	   *joinexpr;
+	RangeTblEntry  *resultRelRTE, *mergeRelRTE;
+	List		   *mergeActionList;
+
+	/* There can't be any outer WITH to worry about */
+	Assert(pstate->p_ctenamespace == NIL);
+
+	qry->commandType = CMD_MERGE;
+	qry->hasRecursive = false;
+
+	/* process the WITH clause independently of all else */
+	if (stmt->withClause)
+	{
+		if (stmt->withClause->recursive)
+			ereport(ERROR,
+					(errcode(ERRCODE_SYNTAX_ERROR),
+					 errmsg("WITH RECURSIVE is not supported for MERGE statement")));
+
+		qry->cteList = transformWithClause(pstate, stmt->withClause);
+		qry->hasModifyingCTE = pstate->p_hasModifyingCTE;
+	}
+
+	/*
+	 * Check WHEN clauses for permissions and sanity
+	 */
+	is_terminal[0] = false;
+	is_terminal[1] = false;
+	foreach(l, stmt->mergeWhenClauses)
+	{
+		MergeWhenClause *mergeWhenClause = (MergeWhenClause *) lfirst(l);
+		int		when_type = (mergeWhenClause->matched ? 0 : 1);
+
+		/*
+		 * Collect action types so we can check Target permissions
+		 */
+		switch (mergeWhenClause->commandType)
+		{
+			case CMD_INSERT:
+				targetPerms |= ACL_INSERT;
+				break;
+			case CMD_UPDATE:
+				targetPerms |= ACL_UPDATE;
+				break;
+			case CMD_DELETE:
+				targetPerms |= ACL_DELETE;
+				break;
+			case CMD_NOTHING:
+				break;
+			default:
+				elog(ERROR, "unknown action in MERGE WHEN clause");
+		}
+
+		/*
+		 * Check for unreachable WHEN clauses
+		 */
+		if (mergeWhenClause->condition == NULL)
+			is_terminal[when_type] = true;
+		else if (is_terminal[when_type])
+			ereport(ERROR,
+					(errcode(ERRCODE_SYNTAX_ERROR),
+					 errmsg("unreachable WHEN clause specified after unconditional WHEN clause")));
+	}
+
+	/*
+	 * Construct a query of the form
+	 * 	SELECT relation.ctid	--junk attribute
+	 *		  ,relation.tableoid	--junk attribute
+	 * 		  ,source_relation.<somecols>
+	 * 		  ,relation.<somecols>
+	 *  FROM relation RIGHT JOIN source_relation
+	 *  ON  join_condition; -- no WHERE clause - all conditions are applied in
+	 * executor
+	 *
+	 * stmt->relation is the target relation, given as a RangeVar
+	 * stmt->source_relation is a RangeVar or subquery
+	 *
+	 * We specify the join as a RIGHT JOIN as a simple way of forcing the
+	 * first (larg) RTE to refer to the target table.
+	 *
+	 * The MERGE query's join can be tuned in some cases, see below for these
+	 * special case tweaks.
+	 *
+	 * We set QSRC_PARSER to show query constructed in parse analysis
+	 *
+	 * Note that we have only one Query for a MERGE statement and the planner
+	 * is called only once. That query is executed once to produce our stream
+	 * of candidate change rows, so the query must contain all of the columns
+	 * required by each of the targetlist or conditions for each action.
+	 *
+	 * As top-level statements INSERT, UPDATE and DELETE have a Query, whereas
+	 * with MERGE the individual actions do not require separate planning,
+	 * only different handling in the executor. See nodeModifyTable handling
+	 * of commandType CMD_MERGE.
+	 *
+	 * A sub-query can include the Target, but otherwise the sub-query cannot
+	 * reference the outermost Target table at all.
+	 */
+	qry->querySource = QSRC_PARSER;
+
+	/*
+	 * Setup the target table. Unlike regular UPDATE/DELETE, we don't expand
+	 * inheritance for the target relation in case of MERGE.
+	 *
+	 * This special arrangement is required for handling partitioned tables
+	 * because we perform an JOIN between the target and the source relation to
+	 * identify the matching and not-matching rows. If we take the usual path
+	 * of expanding the target table's inheritance and create one subplan per
+	 * partition, then we we won't be able to correctly identify the matching
+	 * and not-matching rows since for a given source row, there may not be a
+	 * matching row in one partition, but it may exists in some other
+	 * partition. So we must first append all the qualifying rows from all the
+	 * partitions and then do the matching.
+	 *
+	 * Once a target row is returned by the underlying join, we find the
+	 * correct partition and setup required state to carry out UPDATE/DELETE.
+	 * All of this happens during execution.
+	 */
+	qry->resultRelation = setTargetTable(pstate, stmt->relation,
+										 false,	/* do not expand inheritance */
+										 true, targetPerms);
+
+	/*
+	 * Create a JOIN between the target and the source relation.
+	 */
+	joinexpr = makeNode(JoinExpr);
+	joinexpr->isNatural = false;
+	joinexpr->alias = NULL;
+	joinexpr->usingClause = NIL;
+	joinexpr->quals = stmt->join_condition;
+	joinexpr->larg = (Node *) stmt->relation;
+	joinexpr->rarg = (Node *) stmt->source_relation;
+
+	/*
+	 * Simplify the MERGE query as much as possible
+	 *
+	 * These seem like things that could go into Optimizer, but they are
+	 * semantic simplifications rather than optimizations, per se.
+	 *
+	 * If there are no INSERT actions we won't be using the non-matching
+	 * candidate rows for anything, so no need for an outer join. We do still
+	 * need an inner join for UPDATE and DELETE actions.
+	 */
+	if (targetPerms & ACL_INSERT)
+		joinexpr->jointype = JOIN_RIGHT;
+	else
+		joinexpr->jointype = JOIN_INNER;
+
+	/*
+	 * We use a special purpose transformation here because the normal
+	 * routines don't quite work right for the MERGE case.
+	 *
+	 * A special mergeSourceTargetList is setup by transformMergeJoinClause().
+	 * It refers to all the attributes provided by the source relation. This
+	 * is later used by set_plan_refs() to fix the UPDATE/INSERT target lists
+	 * to so that they can correctly fetch the attributes from the source
+	 * relation.
+	 *
+	 * The target relation when used in the underlying join, gets a new RTE
+	 * with rte->inh set to true. We remember this RTE (and later pass on to
+	 * the planner and executor) for two main reasons:
+	 *
+	 * 1. If we ever need to run EvalPlanQual while performing MERGE, we must
+	 * make the modified tuple available to the underlying join query, which is
+	 * using a different RTE from the resultRelation RTE.
+	 *
+	 * 2. rewriteTargetListMerge() requires the RTE of the underlying join in
+	 * order to add junk CTID and TABLEOID attributes.
+	 */
+	qry->mergeTarget_relation = transformMergeJoinClause(pstate, (Node *) joinexpr,
+														 &qry->mergeSourceTargetList);
+
+	/*
+	 * The target table referenced in the MERGE is looked up twice; once while
+	 * setting it up as the result relation and again when it's used in the
+	 * underlying the join query. In some rare situations, it may happen that
+	 * these lookups return different results, for example, if a new relation
+	 * with the same name gets created in a schema which is ahead in the
+	 * search_path, in between the two lookups.
+	 *
+	 * It's a very narrow case, but nevertheless we guard against it by simply
+	 * checking if the OIDs returned by the two lookups is the same. If not, we
+	 * just throw an error.
+	 */
+	Assert(qry->resultRelation > 0);
+	Assert(qry->mergeTarget_relation > 0);
+
+	/* Fetch both the RTEs */
+	resultRelRTE = rt_fetch(qry->resultRelation, pstate->p_rtable);
+	mergeRelRTE = rt_fetch(qry->mergeTarget_relation, pstate->p_rtable);
+
+	if (resultRelRTE->relid != mergeRelRTE->relid)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("relation referenced by MERGE statement has changed")));
+
+	/*
+	 * This query should just provide the source relation columns. Later, in
+	 * preprocess_targetlist(), we shall also add "ctid" attribute of the
+	 * target relation to ensure that the target tuple can be fetched
+	 * correctly.
+	 */
+	qry->targetList = qry->mergeSourceTargetList;
+
+	/* qry has no WHERE clause so absent quals are shown as NULL */
+	qry->jointree = makeFromExpr(pstate->p_joinlist, NULL);
+	qry->rtable = pstate->p_rtable;
+
+	/*
+	 * XXX MERGE is unsupported in various cases
+	 */
+	if (!(pstate->p_target_relation->rd_rel->relkind == RELKIND_RELATION ||
+		  pstate->p_target_relation->rd_rel->relkind == RELKIND_PARTITIONED_TABLE))
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("MERGE is not supported for this relation type")));
+
+	if (pstate->p_target_relation->rd_rel->relkind != RELKIND_PARTITIONED_TABLE &&
+		pstate->p_target_relation->rd_rel->relhassubclass)
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("MERGE is not supported for relations with inheritance")));
+
+	if (pstate->p_target_relation->rd_rel->relhasrules)
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("MERGE is not supported for relations with rules")));
+
+	/*
+	 * We now have a good query shape, so now look at the when conditions and
+	 * action targetlists.
+	 *
+	 * Overall, the MERGE Query's targetlist is NIL.
+	 *
+	 * Each individual action has its own targetlist that needs separate
+	 * transformation. These transforms don't do anything to the overall
+	 * targetlist, since that is only used for resjunk columns.
+	 *
+	 * We can reference any column in Target or Source, which is OK because
+	 * both of those already have RTEs. There is nothing like the EXCLUDED
+	 * pseudo-relation for INSERT ON CONFLICT.
+	 */
+	mergeActionList = NIL;
+	foreach(l, stmt->mergeWhenClauses)
+	{
+		MergeWhenClause *mergeWhenClause = (MergeWhenClause *) lfirst(l);
+		MergeAction		  *action = makeNode(MergeAction);
+
+		action->commandType = mergeWhenClause->commandType;
+		action->matched = mergeWhenClause->matched;
+
+		/*
+		 * Set namespace for the specific action. This must be done before
+		 * analyzing the WHEN quals and the action targetlisst.
+		 */
+		setNamespaceForMergeWhen(pstate, mergeWhenClause);
+
+		/*
+		 * Transform the when condition.
+		 *
+		 * Note that these quals are NOT added to the join quals; instead they
+		 * are evaluated separately during execution to decide which of the
+		 * WHEN MATCHED or WHEN NOT MATCHED actions to execute.
+		 */
+		action->qual = transformWhereClause(pstate, mergeWhenClause->condition,
+											EXPR_KIND_MERGE_WHEN_AND, "WHEN");
+
+		/*
+		 * Transform target lists for each INSERT and UPDATE action stmt
+		 */
+		switch (action->commandType)
+		{
+			case CMD_INSERT:
+				{
+					List	   *exprList = NIL;
+					ListCell   *lc;
+					RangeTblEntry *rte;
+					ListCell   *icols;
+					ListCell   *attnos;
+					List	   *icolumns;
+					List	   *attrnos;
+
+					pstate->p_is_insert = true;
+
+					icolumns = checkInsertTargets(pstate,
+												  mergeWhenClause->cols,
+												  &attrnos);
+					Assert(list_length(icolumns) == list_length(attrnos));
+
+					action->override = mergeWhenClause->override;
+
+					/*
+					 * Handle INSERT much like in transformInsertStmt
+					 */
+					if (mergeWhenClause->values == NIL)
+					{
+						/*
+						 * We have INSERT ... DEFAULT VALUES.  We can handle
+						 * this case by emitting an empty targetlist --- all
+						 * columns will be defaulted when the planner expands
+						 * the targetlist.
+						 */
+						exprList = NIL;
+					}
+					else
+					{
+						/*
+						 * Process INSERT ... VALUES with a single VALUES
+						 * sublist.  We treat this case separately for
+						 * efficiency.  The sublist is just computed directly
+						 * as the Query's targetlist, with no VALUES RTE.  So
+						 * it works just like a SELECT without any FROM.
+						 */
+
+						/*
+						 * Do basic expression transformation (same as a ROW()
+						 * expr, but allow SetToDefault at top level)
+						 */
+						exprList = transformExpressionList(pstate,
+														   mergeWhenClause->values,
+														   EXPR_KIND_VALUES_SINGLE,
+														   true);
+
+						/* Prepare row for assignment to target table */
+						exprList = transformInsertRow(pstate, exprList,
+													  mergeWhenClause->cols,
+													  icolumns, attrnos,
+													  false);
+					}
+
+					/*
+					 * Generate action's target list using the computed list
+					 * of expressions. Also, mark all the target columns as
+					 * needing insert permissions.
+					 */
+					rte = pstate->p_target_rangetblentry;
+					icols = list_head(icolumns);
+					attnos = list_head(attrnos);
+					foreach(lc, exprList)
+					{
+						Expr	   *expr = (Expr *) lfirst(lc);
+						ResTarget  *col;
+						AttrNumber	attr_num;
+						TargetEntry *tle;
+
+						col = lfirst_node(ResTarget, icols);
+						attr_num = (AttrNumber) lfirst_int(attnos);
+
+						tle = makeTargetEntry(expr,
+											  attr_num,
+											  col->name,
+											  false);
+						action->targetList = lappend(action->targetList, tle);
+
+						rte->insertedCols = bms_add_member(rte->insertedCols,
+														   attr_num - FirstLowInvalidHeapAttributeNumber);
+
+						icols = lnext(icols);
+						attnos = lnext(attnos);
+					}
+				}
+				break;
+			case CMD_UPDATE:
+				{
+					pstate->p_is_insert = false;
+					action->targetList = transformUpdateTargetList(pstate,
+																   mergeWhenClause->targetList);
+				}
+				break;
+			case CMD_DELETE:
+				break;
+
+			case CMD_NOTHING:
+				action->targetList = NIL;
+				break;
+			default:
+				elog(ERROR, "unknown action in MERGE WHEN clause");
+		}
+
+		mergeActionList = lappend(mergeActionList, action);
+	}
+
+	qry->mergeActionList = mergeActionList;
+
+	/* XXX maybe later */
+	qry->returningList = NULL;
+
+	qry->hasTargetSRFs = false;
+	qry->hasSubLinks = pstate->p_hasSubLinks;
+
+	assign_query_collations(pstate, qry);
+
+	return qry;
+}
+
+static void
+setNamespaceVisibilityForRTE(List *namespace, RangeTblEntry *rte,
+							 bool rel_visible,
+							 bool cols_visible)
+{
+	ListCell   *lc;
+
+	foreach(lc, namespace)
+	{
+		ParseNamespaceItem *nsitem = (ParseNamespaceItem *) lfirst(lc);
+
+		if (nsitem->p_rte == rte)
+		{
+			nsitem->p_rel_visible = rel_visible;
+			nsitem->p_cols_visible = cols_visible;
+			break;
+		}
+	}
+
+}
+
+/*
+ * Expand the source relation to include all attributes of this RTE.
+ *
+ * This function is very similar to expandRelAttrs except that we don't mark
+ * columns for SELECT privileges. That will be decided later when we transform
+ * the action targetlists and the WHEN quals for actual references to the
+ * source relation.
+ */
+static List *
+expandSourceTL(ParseState *pstate, RangeTblEntry *rte, int rtindex)
+{
+	List	   *names,
+			   *vars;
+	ListCell   *name,
+			   *var;
+	List	   *te_list = NIL;
+
+	expandRTE(rte, rtindex, 0, -1, false, &names, &vars);
+
+	/*
+	 * Require read access to the table.
+	 */
+	rte->requiredPerms |= ACL_SELECT;
+
+	forboth(name, names, var, vars)
+	{
+		char	   *label = strVal(lfirst(name));
+		Var		   *varnode = (Var *) lfirst(var);
+		TargetEntry *te;
+
+		te = makeTargetEntry((Expr *) varnode,
+							 (AttrNumber) pstate->p_next_resno++,
+							 label,
+							 false);
+		te_list = lappend(te_list, te);
+	}
+
+	Assert(name == NULL && var == NULL);	/* lists not the same length? */
+
+	return te_list;
+}
diff --git a/src/backend/parser/parse_relation.c b/src/backend/parser/parse_relation.c
index 378cbcbf79..1236144e9f 100644
--- a/src/backend/parser/parse_relation.c
+++ b/src/backend/parser/parse_relation.c
@@ -729,6 +729,16 @@ scanRTEForColumn(ParseState *pstate, RangeTblEntry *rte, const char *colname,
 							colname),
 					 parser_errposition(pstate, location)));
 
+		/* In MERGE WHEN AND condition, no system column is allowed except tableOid or OID */
+		if (pstate->p_expr_kind == EXPR_KIND_MERGE_WHEN_AND &&
+			attnum < InvalidAttrNumber &&
+			!(attnum == TableOidAttributeNumber))
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_COLUMN_REFERENCE),
+					 errmsg("system column \"%s\" reference in WHEN AND condition is invalid",
+							colname),
+					 parser_errposition(pstate, location)));
+
 		if (attnum != InvalidAttrNumber)
 		{
 			/* now check to see if column actually is defined */
diff --git a/src/backend/rewrite/rewriteHandler.c b/src/backend/rewrite/rewriteHandler.c
index 43815d26ff..f125b118b7 100644
--- a/src/backend/rewrite/rewriteHandler.c
+++ b/src/backend/rewrite/rewriteHandler.c
@@ -1379,6 +1379,57 @@ rewriteTargetListUD(Query *parsetree, RangeTblEntry *target_rte,
 	}
 }
 
+void
+rewriteTargetListMerge(Query *parsetree, Relation target_relation)
+{
+	Var		   *var = NULL;
+	const char *attrname;
+	TargetEntry *tle;
+
+	Assert(target_relation->rd_rel->relkind == RELKIND_RELATION ||
+		   target_relation->rd_rel->relkind == RELKIND_MATVIEW ||
+		   target_relation->rd_rel->relkind == RELKIND_PARTITIONED_TABLE);
+
+	/*
+	 * Emit CTID so that executor can find the row to update or delete.
+	 */
+	var = makeVar(parsetree->mergeTarget_relation,
+				  SelfItemPointerAttributeNumber,
+				  TIDOID,
+				  -1,
+				  InvalidOid,
+				  0);
+
+	attrname = "ctid";
+	tle = makeTargetEntry((Expr *) var,
+						  list_length(parsetree->targetList) + 1,
+						  pstrdup(attrname),
+						  true);
+
+	parsetree->targetList = lappend(parsetree->targetList, tle);
+
+	/*
+	 * If we are dealing with partitioned table, then emit TABLEOID so that
+	 * executor can find the partition the row belongs to.
+	 */
+	if (target_relation->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
+	{
+		var = makeVar(parsetree->mergeTarget_relation,
+				TableOidAttributeNumber,
+				OIDOID,
+				-1,
+				InvalidOid,
+				0);
+
+		attrname = "tableoid";
+		tle = makeTargetEntry((Expr *) var,
+				list_length(parsetree->targetList) + 1,
+				pstrdup(attrname),
+				true);
+
+		parsetree->targetList = lappend(parsetree->targetList, tle);
+	}
+}
 
 /*
  * matchLocks -
@@ -3455,6 +3506,7 @@ RewriteQuery(Query *parsetree, List *rewrite_events)
 		}
 		else if (event == CMD_UPDATE)
 		{
+			Assert(parsetree->override == OVERRIDING_NOT_SET);
 			parsetree->targetList =
 				rewriteTargetListIU(parsetree->targetList,
 									parsetree->commandType,
@@ -3462,6 +3514,48 @@ RewriteQuery(Query *parsetree, List *rewrite_events)
 									rt_entry_relation,
 									parsetree->resultRelation, NULL);
 		}
+		else if (event == CMD_MERGE)
+		{
+			Assert(parsetree->override == OVERRIDING_NOT_SET);
+
+			/*
+			 * Rewrite each action targetlist separately
+			 */
+			foreach(lc1, parsetree->mergeActionList)
+			{
+				MergeAction *action = (MergeAction *) lfirst(lc1);
+
+				switch (action->commandType)
+				{
+					case CMD_NOTHING:
+					case CMD_DELETE:	/* Nothing to do here */
+						break;
+					case CMD_UPDATE:
+						action->targetList =
+							rewriteTargetListIU(action->targetList,
+												action->commandType,
+												parsetree->override,
+												rt_entry_relation,
+												parsetree->resultRelation,
+												NULL);
+						break;
+					case CMD_INSERT:
+						{
+							action->targetList =
+								rewriteTargetListIU(action->targetList,
+													action->commandType,
+													action->override,
+													rt_entry_relation,
+													parsetree->resultRelation,
+													NULL);
+						}
+						break;
+					default:
+						elog(ERROR, "unrecognized commandType: %d", action->commandType);
+						break;
+				}
+			}
+		}
 		else if (event == CMD_DELETE)
 		{
 			/* Nothing to do here */
@@ -3475,13 +3569,20 @@ RewriteQuery(Query *parsetree, List *rewrite_events)
 		locks = matchLocks(event, rt_entry_relation->rd_rules,
 						   result_relation, parsetree, &hasUpdate);
 
-		product_queries = fireRules(parsetree,
-									result_relation,
-									event,
-									locks,
-									&instead,
-									&returning,
-									&qual_product);
+		/*
+		 * XXX MERGE doesn't support write rules because they would violate
+		 * the SQL Standard spec and would be unclear how they should work.
+		 */
+		if (event == CMD_MERGE)
+			product_queries = NIL;
+		else
+			product_queries = fireRules(parsetree,
+										result_relation,
+										event,
+										locks,
+										&instead,
+										&returning,
+										&qual_product);
 
 		/*
 		 * If there were no INSTEAD rules, and the target relation is a view
diff --git a/src/backend/rewrite/rowsecurity.c b/src/backend/rewrite/rowsecurity.c
index 61ef396d8a..57e52b4f98 100644
--- a/src/backend/rewrite/rowsecurity.c
+++ b/src/backend/rewrite/rowsecurity.c
@@ -379,6 +379,95 @@ get_row_security_policies(Query *root, RangeTblEntry *rte, int rt_index,
 		}
 	}
 
+	/*
+	 * FOR MERGE, we fetch policies for UPDATE, DELETE and INSERT (and ALL)
+	 * and set them up so that we can enforce the appropriate policy depending
+	 * on the final action we take.
+	 *
+	 * We don't fetch the SELECT policies since they are correctly applied to
+	 * the root->mergeTarget_relation. The target rows are selected after
+	 * joining the mergeTarget_relation and the source relation and hence it's
+	 * enough to apply SELECT policies to the mergeTarget_relation.
+	 *
+	 * We don't push the UPDATE/DELETE USING quals to the RTE because we don't
+	 * really want to apply them while scanning the relation since we don't
+	 * know whether we will be doing a UPDATE or a DELETE at the end. We apply
+	 * the respective policy once we decide the final action on the target
+	 * tuple.
+	 *
+	 * XXX We are setting up USING quals as WITH CHECK. If RLS prohibits
+	 * UPDATE/DELETE on the target row, we shall throw an error instead of
+	 * silently ignoring the row. This is different than how normal
+	 * UPDATE/DELETE works and more in line with INSERT ON CONFLICT DO UPDATE
+	 * handling.
+	 */
+	if (commandType == CMD_MERGE)
+	{
+		List	   *merge_permissive_policies;
+		List	   *merge_restrictive_policies;
+
+		/*
+		 * Fetch the UPDATE policies and set them up to execute on the
+		 * existing target row before doing UPDATE.
+		 */
+		get_policies_for_relation(rel, CMD_UPDATE, user_id,
+								  &merge_permissive_policies,
+								  &merge_restrictive_policies);
+
+		/*
+		 * WCO_RLS_MERGE_UPDATE_CHECK is used to check UPDATE USING quals on
+		 * the existing target row.
+		 */
+		add_with_check_options(rel, rt_index,
+							   WCO_RLS_MERGE_UPDATE_CHECK,
+							   merge_permissive_policies,
+							   merge_restrictive_policies,
+							   withCheckOptions,
+							   hasSubLinks,
+							   true);
+
+		/*
+		 * Same with DELETE policies.
+		 */
+		get_policies_for_relation(rel, CMD_DELETE, user_id,
+								  &merge_permissive_policies,
+								  &merge_restrictive_policies);
+
+		add_with_check_options(rel, rt_index,
+							   WCO_RLS_MERGE_DELETE_CHECK,
+							   merge_permissive_policies,
+							   merge_restrictive_policies,
+							   withCheckOptions,
+							   hasSubLinks,
+							   true);
+
+		/*
+		 * No special handling is required for INSERT policies. They will be
+		 * checked and enforced during ExecInsert(). But we must add them to
+		 * withCheckOptions.
+		 */
+		get_policies_for_relation(rel, CMD_INSERT, user_id,
+								  &merge_permissive_policies,
+								  &merge_restrictive_policies);
+
+		add_with_check_options(rel, rt_index,
+							   WCO_RLS_INSERT_CHECK,
+							   merge_permissive_policies,
+							   merge_restrictive_policies,
+							   withCheckOptions,
+							   hasSubLinks,
+							   false);
+
+		/* Enforce the WITH CHECK clauses of the UPDATE policies */
+		add_with_check_options(rel, rt_index,
+							   WCO_RLS_UPDATE_CHECK,
+							   merge_permissive_policies,
+							   merge_restrictive_policies,
+							   withCheckOptions,
+							   hasSubLinks,
+							   false);
+	}
+
 	heap_close(rel, NoLock);
 
 	/*
@@ -438,6 +527,14 @@ get_policies_for_relation(Relation relation, CmdType cmd, Oid user_id,
 					if (policy->polcmd == ACL_DELETE_CHR)
 						cmd_matches = true;
 					break;
+				case CMD_MERGE:
+
+					/*
+					 * We do not support a separate policy for MERGE command.
+					 * Instead it derives from the policies defined for other
+					 * commands.
+					 */
+					break;
 				default:
 					elog(ERROR, "unrecognized policy command type %d",
 						 (int) cmd);
diff --git a/src/backend/tcop/pquery.c b/src/backend/tcop/pquery.c
index 519c763f38..fa1ac3fcc5 100644
--- a/src/backend/tcop/pquery.c
+++ b/src/backend/tcop/pquery.c
@@ -191,6 +191,11 @@ ProcessQuery(PlannedStmt *plan,
 						 "DELETE " UINT64_FORMAT,
 						 queryDesc->estate->es_processed);
 				break;
+			case CMD_MERGE:
+				snprintf(completionTag, COMPLETION_TAG_BUFSIZE,
+						 "MERGE " UINT64_FORMAT,
+						 queryDesc->estate->es_processed);
+				break;
 			default:
 				strcpy(completionTag, "???");
 				break;
diff --git a/src/backend/tcop/utility.c b/src/backend/tcop/utility.c
index 970c94ee80..527f40be61 100644
--- a/src/backend/tcop/utility.c
+++ b/src/backend/tcop/utility.c
@@ -112,6 +112,7 @@ CommandIsReadOnly(PlannedStmt *pstmt)
 		case CMD_UPDATE:
 		case CMD_INSERT:
 		case CMD_DELETE:
+		case CMD_MERGE:
 			return false;
 		case CMD_UTILITY:
 			/* For now, treat all utility commands as read/write */
@@ -1859,6 +1860,8 @@ QueryReturnsTuples(Query *parsetree)
 		case CMD_SELECT:
 			/* returns tuples */
 			return true;
+		case CMD_MERGE:
+			return false;
 		case CMD_INSERT:
 		case CMD_UPDATE:
 		case CMD_DELETE:
@@ -2103,6 +2106,10 @@ CreateCommandTag(Node *parsetree)
 			tag = "UPDATE";
 			break;
 
+		case T_MergeStmt:
+			tag = "MERGE";
+			break;
+
 		case T_SelectStmt:
 			tag = "SELECT";
 			break;
@@ -2846,6 +2853,9 @@ CreateCommandTag(Node *parsetree)
 					case CMD_DELETE:
 						tag = "DELETE";
 						break;
+					case CMD_MERGE:
+						tag = "MERGE";
+						break;
 					case CMD_UTILITY:
 						tag = CreateCommandTag(stmt->utilityStmt);
 						break;
@@ -2906,6 +2916,9 @@ CreateCommandTag(Node *parsetree)
 					case CMD_DELETE:
 						tag = "DELETE";
 						break;
+					case CMD_MERGE:
+						tag = "MERGE";
+						break;
 					case CMD_UTILITY:
 						tag = CreateCommandTag(stmt->utilityStmt);
 						break;
@@ -2954,6 +2967,7 @@ GetCommandLogLevel(Node *parsetree)
 		case T_InsertStmt:
 		case T_DeleteStmt:
 		case T_UpdateStmt:
+		case T_MergeStmt:
 			lev = LOGSTMT_MOD;
 			break;
 
@@ -3393,6 +3407,7 @@ GetCommandLogLevel(Node *parsetree)
 					case CMD_UPDATE:
 					case CMD_INSERT:
 					case CMD_DELETE:
+					case CMD_MERGE:
 						lev = LOGSTMT_MOD;
 						break;
 
@@ -3423,6 +3438,7 @@ GetCommandLogLevel(Node *parsetree)
 					case CMD_UPDATE:
 					case CMD_INSERT:
 					case CMD_DELETE:
+					case CMD_MERGE:
 						lev = LOGSTMT_MOD;
 						break;
 
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index 7993c05283..42e9740cfc 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -473,6 +473,20 @@ static const SchemaQuery Query_for_list_of_updatables = {
 	.result = "pg_catalog.quote_ident(c.relname)",
 };
 
+/* Relations supporting MERGE */
+static const SchemaQuery Query_for_list_of_mergetargets = {
+	.catname = "pg_catalog.pg_class c",
+	.selcondition =
+	"c.relkind IN (" CppAsString2(RELKIND_RELATION) ", "
+	CppAsString2(RELKIND_PARTITIONED_TABLE) ") AND "
+	"c.relhasrules = false AND "
+	"(c.relhassubclass = false OR "
+	" c.relkind = " CppAsString2(RELKIND_PARTITIONED_TABLE) ")",
+	.viscondition = "pg_catalog.pg_table_is_visible(c.oid)",
+	.namespace = "c.relnamespace",
+	.result = "pg_catalog.quote_ident(c.relname)",
+};
+
 /* Relations supporting SELECT */
 static const SchemaQuery Query_for_list_of_selectables = {
 	.catname = "pg_catalog.pg_class c",
@@ -1316,7 +1330,7 @@ psql_completion(const char *text, int start, int end)
 		"COMMENT", "COMMIT", "COPY", "CREATE", "DEALLOCATE", "DECLARE",
 		"DELETE FROM", "DISCARD", "DO", "DROP", "END", "EXECUTE", "EXPLAIN",
 		"FETCH", "GRANT", "IMPORT", "INSERT", "LISTEN", "LOAD", "LOCK",
-		"MOVE", "NOTIFY", "PREPARE",
+		"MERGE", "MOVE", "NOTIFY", "PREPARE",
 		"REASSIGN", "REFRESH MATERIALIZED VIEW", "REINDEX", "RELEASE",
 		"RESET", "REVOKE", "ROLLBACK",
 		"SAVEPOINT", "SECURITY LABEL", "SELECT", "SET", "SHOW", "START",
@@ -2766,8 +2780,8 @@ psql_completion(const char *text, int start, int end)
  * EXPLAIN [ ANALYZE ] [ VERBOSE ] statement
  */
 	else if (Matches("EXPLAIN"))
-		COMPLETE_WITH("SELECT", "INSERT", "DELETE", "UPDATE", "DECLARE",
-					  "ANALYZE", "VERBOSE");
+		COMPLETE_WITH("SELECT", "INSERT", "DELETE", "UPDATE", "MERGE",
+					  "DECLARE", "ANALYZE", "VERBOSE");
 	else if (HeadMatches("EXPLAIN", "(*") &&
 			 !HeadMatches("EXPLAIN", "(*)"))
 	{
@@ -2785,12 +2799,13 @@ psql_completion(const char *text, int start, int end)
 			COMPLETE_WITH("TEXT", "XML", "JSON", "YAML");
 	}
 	else if (Matches("EXPLAIN", "ANALYZE"))
-		COMPLETE_WITH("SELECT", "INSERT", "DELETE", "UPDATE", "DECLARE",
-					  "VERBOSE");
+		COMPLETE_WITH("SELECT", "INSERT", "DELETE", "UPDATE", "MERGE",
+					  "DECLARE", "VERBOSE");
 	else if (Matches("EXPLAIN", "(*)") ||
 			 Matches("EXPLAIN", "VERBOSE") ||
 			 Matches("EXPLAIN", "ANALYZE", "VERBOSE"))
-		COMPLETE_WITH("SELECT", "INSERT", "DELETE", "UPDATE", "DECLARE");
+		COMPLETE_WITH("SELECT", "INSERT", "DELETE", "UPDATE", "MERGE",
+					  "DECLARE");
 
 /* FETCH && MOVE */
 	/* Complete FETCH with one of FORWARD, BACKWARD, RELATIVE */
@@ -3012,6 +3027,9 @@ psql_completion(const char *text, int start, int end)
 		COMPLETE_WITH("SCHEMA");
 
 /* INSERT --- can be inside EXPLAIN, RULE, etc */
+	/* Complete NOT MATCHED THEN INSERT */
+	else if (TailMatches("NOT", "MATCHED", "THEN", "INSERT"))
+		COMPLETE_WITH("VALUES", "(");
 	/* Complete INSERT with "INTO" */
 	else if (TailMatches("INSERT"))
 		COMPLETE_WITH("INTO");
@@ -3083,6 +3101,55 @@ psql_completion(const char *text, int start, int end)
 			 Matches("LOCK", "TABLE", MatchAny, "IN", "SHARE"))
 		COMPLETE_WITH("MODE", "ROW EXCLUSIVE MODE",
 					  "UPDATE EXCLUSIVE MODE");
+/* MERGE --- can be inside EXPLAIN */
+	else if (TailMatches("MERGE"))
+		COMPLETE_WITH("INTO");
+	else if (TailMatches("MERGE", "INTO"))
+		COMPLETE_WITH_SCHEMA_QUERY(Query_for_list_of_mergetargets, NULL);
+	else if (TailMatches("MERGE", "INTO", MatchAny))
+		COMPLETE_WITH("USING", "AS");
+	else if (TailMatches("MERGE", "INTO", MatchAny, "USING"))
+		COMPLETE_WITH_SCHEMA_QUERY(Query_for_list_of_tables, NULL);
+	/* with [AS] alias */
+	else if (TailMatches("MERGE", "INTO", MatchAny, "AS", MatchAny))
+		COMPLETE_WITH("USING");
+	else if (TailMatches("MERGE", "INTO", MatchAny, MatchAny))
+		COMPLETE_WITH("USING");
+	else if (TailMatches("MERGE", "INTO", MatchAny, "AS", MatchAny, "USING"))
+		COMPLETE_WITH_SCHEMA_QUERY(Query_for_list_of_tables, NULL);
+	else if (TailMatches("MERGE", "INTO", MatchAny, MatchAny, "USING"))
+		COMPLETE_WITH_SCHEMA_QUERY(Query_for_list_of_tables, NULL);
+	/* ON */
+	else if (TailMatches("MERGE", "INTO", MatchAny, "USING", MatchAny))
+		COMPLETE_WITH("ON");
+	else if (TailMatches("INTO", MatchAny, "AS", MatchAny, "USING", MatchAny, "AS", MatchAny))
+		COMPLETE_WITH("ON");
+	else if (TailMatches("INTO", MatchAny, MatchAny, "USING", MatchAny, MatchAny))
+		COMPLETE_WITH("ON");
+	/* ON condition */
+	else if (TailMatches("INTO", MatchAny, "USING", MatchAny, "ON"))
+		COMPLETE_WITH_ATTR(prev4_wd, "");
+	else if (TailMatches("INTO", MatchAny, "AS", MatchAny, "USING", MatchAny, "AS", MatchAny, "ON"))
+		COMPLETE_WITH_ATTR(prev8_wd, "");
+	else if (TailMatches("INTO", MatchAny, MatchAny, "USING", MatchAny, MatchAny, "ON"))
+		COMPLETE_WITH_ATTR(prev6_wd, "");
+	/* WHEN [NOT] MATCHED */
+	else if (TailMatches("USING", MatchAny, "ON", MatchAny))
+		COMPLETE_WITH("WHEN MATCHED", "WHEN NOT MATCHED");
+	else if (TailMatches("USING", MatchAny, "AS", MatchAny, "ON", MatchAny))
+		COMPLETE_WITH("WHEN MATCHED", "WHEN NOT MATCHED");
+	else if (TailMatches("USING", MatchAny, MatchAny, "ON", MatchAny))
+		COMPLETE_WITH("WHEN MATCHED", "WHEN NOT MATCHED");
+	else if (TailMatches("WHEN", "MATCHED"))
+		COMPLETE_WITH("THEN", "AND");
+	else if (TailMatches("WHEN", "NOT", "MATCHED"))
+		COMPLETE_WITH("THEN", "AND");
+	else if (TailMatches("WHEN", "MATCHED", "THEN"))
+		COMPLETE_WITH("UPDATE", "DELETE");
+	else if (TailMatches("WHEN", "NOT", "MATCHED", "THEN"))
+		COMPLETE_WITH("INSERT", "DO");
+	else if (TailMatches("WHEN", "NOT", "MATCHED", "THEN", "DO"))
+		COMPLETE_WITH("NOTHING");
 
 /* NOTIFY --- can be inside EXPLAIN, RULE, etc */
 	else if (TailMatches("NOTIFY"))
diff --git a/src/include/access/heapam.h b/src/include/access/heapam.h
index 64cfdbd2f0..49cb75c2d8 100644
--- a/src/include/access/heapam.h
+++ b/src/include/access/heapam.h
@@ -54,23 +54,34 @@ typedef enum LockTupleMode
  * When heap_update, heap_delete, or heap_lock_tuple fail because the target
  * tuple is already outdated, they fill in this struct to provide information
  * to the caller about what happened.
+ *
+ * result is the result of HeapTupleSatisfiesUpdate, leading to the failure.
+ * It's set to HeapTupleMayBeUpdated when there is no failure.
+ *
  * ctid is the target's ctid link: it is the same as the target's TID if the
  * target was deleted, or the location of the replacement tuple if the target
  * was updated.
+ *
  * xmax is the outdating transaction's XID.  If the caller wants to visit the
  * replacement tuple, it must check that this matches before believing the
  * replacement is really a match.
+ *
  * cmax is the outdating command's CID, but only when the failure code is
  * HeapTupleSelfUpdated (i.e., something in the current transaction outdated
  * the tuple); otherwise cmax is zero.  (We make this restriction because
  * HeapTupleHeaderGetCmax doesn't work for tuples outdated in other
  * transactions.)
+ *
+ * lockmode is only relevant for callers of heap_update() and is the mode which
+ * the caller should use in case it needs to lock the updated tuple.
  */
 typedef struct HeapUpdateFailureData
 {
+	HTSU_Result result;
 	ItemPointerData ctid;
 	TransactionId xmax;
 	CommandId	cmax;
+	LockTupleMode	lockmode;
 } HeapUpdateFailureData;
 
 
@@ -163,7 +174,7 @@ extern void heap_abort_speculative(Relation relation, HeapTuple tuple);
 extern HTSU_Result heap_update(Relation relation, ItemPointer otid,
 			HeapTuple newtup,
 			CommandId cid, Snapshot crosscheck, bool wait,
-			HeapUpdateFailureData *hufd, LockTupleMode *lockmode);
+			HeapUpdateFailureData *hufd);
 extern HTSU_Result heap_lock_tuple(Relation relation, HeapTuple tuple,
 				CommandId cid, LockTupleMode mode, LockWaitPolicy wait_policy,
 				bool follow_update,
diff --git a/src/include/commands/trigger.h b/src/include/commands/trigger.h
index 1031448c14..e980afea4b 100644
--- a/src/include/commands/trigger.h
+++ b/src/include/commands/trigger.h
@@ -207,7 +207,8 @@ extern bool ExecBRDeleteTriggers(EState *estate,
 					 ResultRelInfo *relinfo,
 					 ItemPointer tupleid,
 					 HeapTuple fdw_trigtuple,
-					 TupleTableSlot **epqslot);
+					 TupleTableSlot **epqslot,
+					 HeapUpdateFailureData *hufdp);
 extern void ExecARDeleteTriggers(EState *estate,
 					 ResultRelInfo *relinfo,
 					 ItemPointer tupleid,
@@ -226,7 +227,8 @@ extern TupleTableSlot *ExecBRUpdateTriggers(EState *estate,
 					 ResultRelInfo *relinfo,
 					 ItemPointer tupleid,
 					 HeapTuple fdw_trigtuple,
-					 TupleTableSlot *slot);
+					 TupleTableSlot *slot,
+					 HeapUpdateFailureData *hufdp);
 extern void ExecARUpdateTriggers(EState *estate,
 					 ResultRelInfo *relinfo,
 					 ItemPointer tupleid,
diff --git a/src/include/executor/execMerge.h b/src/include/executor/execMerge.h
new file mode 100644
index 0000000000..5ea8c4e50a
--- /dev/null
+++ b/src/include/executor/execMerge.h
@@ -0,0 +1,31 @@
+/*-------------------------------------------------------------------------
+ *
+ * execMerge.h
+ *
+ *
+ * Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/executor/execMerge.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef EXECMERGE_H
+#define EXECMERGE_H
+
+#include "nodes/execnodes.h"
+
+/* flags for mt_merge_subcommands */
+#define MERGE_INSERT	0x01
+#define MERGE_UPDATE	0x02
+#define MERGE_DELETE	0x04
+
+extern void ExecMerge(ModifyTableState *mtstate, EState *estate,
+					  TupleTableSlot *slot, JunkFilter *junkfilter,
+					  ResultRelInfo *resultRelInfo);
+
+extern void ExecInitMerge(ModifyTableState *mtstate,
+						  EState *estate,
+						  ResultRelInfo *resultRelInfo);
+
+#endif							/* NODEMERGE_H */
diff --git a/src/include/executor/execPartition.h b/src/include/executor/execPartition.h
index d3cfb55f9f..8d4076b3ea 100644
--- a/src/include/executor/execPartition.h
+++ b/src/include/executor/execPartition.h
@@ -149,5 +149,10 @@ extern PartitionPruneState *ExecCreatePartitionPruneState(PlanState *planstate,
 extern Bitmapset *ExecFindMatchingSubPlans(PartitionPruneState *prunestate);
 extern Bitmapset *ExecFindInitialMatchingSubPlans(PartitionPruneState *prunestate,
 								int nsubplans);
+extern ResultRelInfo *ExecFindPartitionByOid(ModifyTableState *mtstate,
+					   ResultRelInfo *rootResultRelInfo,
+					   PartitionTupleRouting *proute,
+					   EState *estate,
+					   Oid partoid);
 
 #endif							/* EXECPARTITION_H */
diff --git a/src/include/executor/instrument.h b/src/include/executor/instrument.h
index 6d0efa7222..e7b70e3ce4 100644
--- a/src/include/executor/instrument.h
+++ b/src/include/executor/instrument.h
@@ -57,7 +57,10 @@ typedef struct Instrumentation
 	double		startup;		/* Total startup time (in seconds) */
 	double		total;			/* Total total time (in seconds) */
 	double		ntuples;		/* Total tuples produced */
-	double		ntuples2;		/* Secondary node-specific tuple counter */
+	/* Additional node-specific tuple counters */
+	double		node_ntuples1;
+	double		node_ntuples2;
+	double		node_ntuples3;
 	double		nloops;			/* # of run cycles for this node */
 	double		nfiltered1;		/* # tuples removed by scanqual or joinqual */
 	double		nfiltered2;		/* # tuples removed by "other" quals */
diff --git a/src/include/executor/nodeModifyTable.h b/src/include/executor/nodeModifyTable.h
index 0d7e579e1c..b7fc31f640 100644
--- a/src/include/executor/nodeModifyTable.h
+++ b/src/include/executor/nodeModifyTable.h
@@ -18,5 +18,29 @@
 extern ModifyTableState *ExecInitModifyTable(ModifyTable *node, EState *estate, int eflags);
 extern void ExecEndModifyTable(ModifyTableState *node);
 extern void ExecReScanModifyTable(ModifyTableState *node);
+extern TupleTableSlot *ExecPrepareTupleRouting(ModifyTableState *mtstate,
+						EState *estate,
+						struct PartitionTupleRouting *proute,
+						ResultRelInfo *targetRelInfo,
+						TupleTableSlot *slot);
+extern TupleTableSlot *
+ExecDelete(ModifyTableState *mtstate, ItemPointer tupleid, HeapTuple oldtuple,
+		   TupleTableSlot *planSlot, EPQState *epqstate, EState *estate,
+		   bool processReturning, bool canSetTag, bool changingPart,
+		   bool *tupleDeleted, TupleTableSlot **epqslot,
+		   HeapUpdateFailureData *hufdp, MergeActionState *actionState);
+extern TupleTableSlot *ExecUpdate(ModifyTableState *mtstate,
+		   ItemPointer tupleid, HeapTuple oldtuple, TupleTableSlot *slot,
+		   TupleTableSlot *planSlot, EPQState *epqstate, EState *estate,
+		   bool *tuple_updated, HeapUpdateFailureData *hufdp,
+		   MergeActionState *actionState, bool canSetTag);
+extern TupleTableSlot *ExecInsert(ModifyTableState *mtstate,
+		   TupleTableSlot *slot,
+		   TupleTableSlot *planSlot,
+		   EState *estate,
+		   MergeActionState *actionState,
+		   bool canSetTag);
+extern void ExecCheckPlanOutput(Relation resultRel, List *targetList);
+extern ResultRelInfo * getTargetResultRelInfo(ModifyTableState *node);
 
 #endif							/* NODEMODIFYTABLE_H */
diff --git a/src/include/executor/spi.h b/src/include/executor/spi.h
index d2616968ac..d12ec0f813 100644
--- a/src/include/executor/spi.h
+++ b/src/include/executor/spi.h
@@ -64,6 +64,7 @@ typedef struct _SPI_plan *SPIPlanPtr;
 #define SPI_OK_REL_REGISTER		15
 #define SPI_OK_REL_UNREGISTER	16
 #define SPI_OK_TD_REGISTER		17
+#define SPI_OK_MERGE			18
 
 #define SPI_OPT_NONATOMIC		(1 << 0)
 
diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
index 5ed0f40f69..ccd2d5c66b 100644
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -367,8 +367,17 @@ typedef struct JunkFilter
 	AttrNumber *jf_cleanMap;
 	TupleTableSlot *jf_resultSlot;
 	AttrNumber	jf_junkAttNo;
+	AttrNumber	jf_otherJunkAttNo;
 } JunkFilter;
 
+typedef struct MergeState
+{
+	/* List of MERGE MATCHED action states */
+	List		   *matchedActionStates;
+	/* List of MERGE NOT MATCHED action states */
+	List		   *notMatchedActionStates;
+} MergeState;
+
 /*
  * OnConflictSetState
  *
@@ -472,8 +481,39 @@ typedef struct ResultRelInfo
 
 	/* Additional information specific to partition tuple routing */
 	struct PartitionRoutingInfo *ri_PartitionInfo;
+
+	int         ri_PartitionLeafIndex;
+
+	/* for running MERGE on this result relation */
+	MergeState *ri_mergeState;
+
+	/*
+	 * While executing MERGE, the target relation is processed twice; once
+	 * as a target relation and once to run a join between the target and the
+	 * source. We generate two different RTEs for these two purposes, one with
+	 * rte->inh set to false and other with rte->inh set to true.
+	 *
+	 * Since the plan re-evaluated by EvalPlanQual uses the join RTE, we must
+	 * install the updated tuple in the scan corresponding to that RTE. The
+	 * following member tracks the index of the second RTE for EvalPlanQual
+	 * purposes. ri_mergeTargetRTI is non-zero only when MERGE is in-progress.
+	 * We use ri_mergeTargetRTI to run EvalPlanQual for MERGE and
+	 * ri_RangeTableIndex elsewhere.
+	 */
+	Index		ri_mergeTargetRTI;
 } ResultRelInfo;
 
+/*
+ * Get the Range table index for EvalPlanQual.
+ *
+ * We use the ri_mergeTargetRTI if set, otherwise use ri_RangeTableIndex.
+ * ri_mergeTargetRTI should really be ever set iff we're running MERGE.
+ */
+#define GetEPQRangeTableIndex(r) \
+	(((r)->ri_mergeTargetRTI > 0)  \
+	 ? (r)->ri_mergeTargetRTI \
+	 : (r)->ri_RangeTableIndex)
+
 /* ----------------
  *	  EState information
  *
@@ -1026,10 +1066,20 @@ typedef struct PlanState
 #define outerPlanState(node)		(((PlanState *)(node))->lefttree)
 
 /* Macros for inline access to certain instrumentation counters */
-#define InstrCountTuples2(node, delta) \
+#define InstrCountNodeTuples1(node, delta) \
+	do { \
+		if (((PlanState *)(node))->instrument) \
+			((PlanState *)(node))->instrument->node_ntuples1 += (delta); \
+	} while (0)
+#define InstrCountNodeTuples2(node, delta) \
 	do { \
 		if (((PlanState *)(node))->instrument) \
-			((PlanState *)(node))->instrument->ntuples2 += (delta); \
+			((PlanState *)(node))->instrument->node_ntuples2 += (delta); \
+	} while (0)
+#define InstrCountNodeTuples3(node, delta) \
+	do { \
+		if (((PlanState *)(node))->instrument) \
+			((PlanState *)(node))->instrument->node_ntuples3 += (delta); \
 	} while (0)
 #define InstrCountFiltered1(node, delta) \
 	do { \
@@ -1087,6 +1137,20 @@ typedef struct ProjectSetState
 	MemoryContext argcontext;	/* context for SRF arguments */
 } ProjectSetState;
 
+/* ----------------
+ *	 MergeActionState information
+ * ----------------
+ */
+typedef struct MergeActionState
+{
+	NodeTag		type;
+	bool		matched;		/* true=MATCHED, false=NOT MATCHED */
+	ExprState  *whenqual;		/* WHEN AND conditions */
+	CmdType		commandType;	/* INSERT/UPDATE/DELETE/DO NOTHING */
+	ProjectionInfo *proj;		/* tuple projection info */
+	TupleDesc	tupDesc;		/* tuple descriptor for projection */
+} MergeActionState;
+
 /* ----------------
  *	 ModifyTableState information
  * ----------------
@@ -1094,7 +1158,7 @@ typedef struct ProjectSetState
 typedef struct ModifyTableState
 {
 	PlanState	ps;				/* its first field is NodeTag */
-	CmdType		operation;		/* INSERT, UPDATE, or DELETE */
+	CmdType		operation;		/* INSERT, UPDATE, DELETE or MERGE */
 	bool		canSetTag;		/* do we set the command tag/es_processed? */
 	bool		mt_done;		/* are we done? */
 	PlanState **mt_plans;		/* subplans (one per target rel) */
@@ -1118,6 +1182,8 @@ typedef struct ModifyTableState
 	 */
 	TupleTableSlot *mt_root_tuple_slot;
 
+	TupleTableSlot *mt_mergeproj;	/* MERGE action projection target */
+
 	/* Tuple-routing support info */
 	struct PartitionTupleRouting *mt_partition_tuple_routing;
 
@@ -1129,6 +1195,9 @@ typedef struct ModifyTableState
 
 	/* Per plan map for tuple conversion from child to root */
 	TupleConversionMap **mt_per_subplan_tupconv_maps;
+
+	/* Flags showing which subcommands are present INS/UPD/DEL/DO NOTHING */
+	int			mt_merge_subcommands;
 } ModifyTableState;
 
 /* ----------------
diff --git a/src/include/nodes/nodes.h b/src/include/nodes/nodes.h
index cac6ff0eda..9774cb123e 100644
--- a/src/include/nodes/nodes.h
+++ b/src/include/nodes/nodes.h
@@ -101,6 +101,7 @@ typedef enum NodeTag
 	T_PlanState,
 	T_ResultState,
 	T_ProjectSetState,
+	T_MergeActionState,
 	T_ModifyTableState,
 	T_AppendState,
 	T_MergeAppendState,
@@ -271,6 +272,7 @@ typedef enum NodeTag
 	T_RollupData,
 	T_GroupingSetData,
 	T_StatisticExtInfo,
+	T_MergeAction,
 
 	/*
 	 * TAGS FOR MEMORY NODES (memnodes.h)
@@ -311,6 +313,7 @@ typedef enum NodeTag
 	T_InsertStmt,
 	T_DeleteStmt,
 	T_UpdateStmt,
+	T_MergeStmt,
 	T_SelectStmt,
 	T_AlterTableStmt,
 	T_AlterTableCmd,
@@ -475,6 +478,7 @@ typedef enum NodeTag
 	T_PartitionRangeDatum,
 	T_PartitionCmd,
 	T_VacuumRelation,
+	T_MergeWhenClause,
 
 	/*
 	 * TAGS FOR REPLICATION GRAMMAR PARSE NODES (replnodes.h)
@@ -663,7 +667,8 @@ typedef enum CmdType
 	CMD_SELECT,					/* select stmt */
 	CMD_UPDATE,					/* update stmt */
 	CMD_INSERT,					/* insert stmt */
-	CMD_DELETE,
+	CMD_DELETE,					/* delete stmt */
+	CMD_MERGE,					/* merge stmt */
 	CMD_UTILITY,				/* cmds like create, destroy, copy, vacuum,
 								 * etc. */
 	CMD_NOTHING					/* dummy command for instead nothing rules
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index e5bdc1cec5..c653d5c96b 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -40,7 +40,7 @@ typedef enum OverridingKind
 typedef enum QuerySource
 {
 	QSRC_ORIGINAL,				/* original parsetree (explicit query) */
-	QSRC_PARSER,				/* added by parse analysis (now unused) */
+	QSRC_PARSER,				/* added by parse analysis in MERGE */
 	QSRC_INSTEAD_RULE,			/* added by unconditional INSTEAD rule */
 	QSRC_QUAL_INSTEAD_RULE,		/* added by conditional INSTEAD rule */
 	QSRC_NON_INSTEAD_RULE		/* added by non-INSTEAD rule */
@@ -109,7 +109,7 @@ typedef struct Query
 {
 	NodeTag		type;
 
-	CmdType		commandType;	/* select|insert|update|delete|utility */
+	CmdType		commandType;	/* select|insert|update|delete|merge|utility */
 
 	QuerySource querySource;	/* where did I come from? */
 
@@ -120,7 +120,7 @@ typedef struct Query
 	Node	   *utilityStmt;	/* non-null if commandType == CMD_UTILITY */
 
 	int			resultRelation; /* rtable index of target relation for
-								 * INSERT/UPDATE/DELETE; 0 for SELECT */
+								 * INSERT/UPDATE/DELETE/MERGE; 0 for SELECT */
 
 	bool		hasAggs;		/* has aggregates in tlist or havingQual */
 	bool		hasWindowFuncs; /* has window functions in tlist */
@@ -170,6 +170,9 @@ typedef struct Query
 
 	List	   *withCheckOptions;	/* a list of WithCheckOption's (added
 									 * during rewrite) */
+	int			mergeTarget_relation;
+	List	   *mergeSourceTargetList;
+	List	   *mergeActionList;	/* list of actions for MERGE (only) */
 
 	/*
 	 * The following two fields identify the portion of the source text string
@@ -1142,7 +1145,9 @@ typedef enum WCOKind
 	WCO_VIEW_CHECK,				/* WCO on an auto-updatable view */
 	WCO_RLS_INSERT_CHECK,		/* RLS INSERT WITH CHECK policy */
 	WCO_RLS_UPDATE_CHECK,		/* RLS UPDATE WITH CHECK policy */
-	WCO_RLS_CONFLICT_CHECK		/* RLS ON CONFLICT DO UPDATE USING policy */
+	WCO_RLS_CONFLICT_CHECK,		/* RLS ON CONFLICT DO UPDATE USING policy */
+	WCO_RLS_MERGE_UPDATE_CHECK, /* RLS MERGE UPDATE USING policy */
+	WCO_RLS_MERGE_DELETE_CHECK	/* RLS MERGE DELETE USING policy */
 } WCOKind;
 
 typedef struct WithCheckOption
@@ -1517,6 +1522,46 @@ typedef struct UpdateStmt
 	WithClause *withClause;		/* WITH clause */
 } UpdateStmt;
 
+/* ----------------------
+ *		Merge Statement
+ * ----------------------
+ */
+typedef struct MergeStmt
+{
+	NodeTag		type;
+	RangeVar   *relation;			/* target relation to merge into */
+	Node	   *source_relation;	/* source relation */
+	Node	   *join_condition; /* join condition between source and target */
+	List	   *mergeWhenClauses;	/* list of MergeWhenClause(es) */
+	WithClause *withClause;		/* WITH clause */
+} MergeStmt;
+
+typedef struct MergeWhenClause
+{
+	NodeTag		type;
+	bool		matched;		/* true=MATCHED, false=NOT MATCHED */
+	CmdType		commandType;	/* INSERT/UPDATE/DELETE/DO NOTHING */
+	Node	   *condition;		/* WHEN AND conditions (raw parser) */
+	List	   *targetList;		/* INSERT/UPDATE targetlist */
+	/* the following members are only useful for INSERT action */
+	List	   *cols;			/* optional: names of the target columns */
+	List	   *values;			/* VALUES to INSERT, or NULL */
+	OverridingKind override;	/* OVERRIDING clause */
+} MergeWhenClause;
+
+/*
+ * WHEN [NOT] MATCHED THEN action info
+ */
+typedef struct MergeAction
+{
+	NodeTag     type;
+	bool        matched;        /* true=MATCHED, false=NOT MATCHED */
+	OverridingKind	override;	/* OVERRIDING clause */
+	Node       *qual;           /* transformed WHEN AND conditions */
+	CmdType     commandType;    /* INSERT/UPDATE/DELETE/DO NOTHING */
+	List       *targetList;     /* the target list (of ResTarget) */
+} MergeAction;
+
 /* ----------------------
  *		Select Statement
  *
diff --git a/src/include/nodes/plannodes.h b/src/include/nodes/plannodes.h
index f116bc23ff..c8f730c5a5 100644
--- a/src/include/nodes/plannodes.h
+++ b/src/include/nodes/plannodes.h
@@ -19,6 +19,7 @@
 #include "lib/stringinfo.h"
 #include "nodes/bitmapset.h"
 #include "nodes/lockoptions.h"
+#include "nodes/parsenodes.h"
 #include "nodes/primnodes.h"
 
 
@@ -43,7 +44,7 @@ typedef struct PlannedStmt
 {
 	NodeTag		type;
 
-	CmdType		commandType;	/* select|insert|update|delete|utility */
+	CmdType		commandType;	/* select|insert|update|delete|merge|utility */
 
 	uint64		queryId;		/* query identifier (copied from Query) */
 
@@ -216,12 +217,13 @@ typedef struct ProjectSet
 typedef struct ModifyTable
 {
 	Plan		plan;
-	CmdType		operation;		/* INSERT, UPDATE, or DELETE */
+	CmdType		operation;		/* INSERT, UPDATE, DELETE or MERGE */
 	bool		canSetTag;		/* do we set the command tag/es_processed? */
 	Index		nominalRelation;	/* Parent RT index for use of EXPLAIN */
 	Index		rootRelation;	/* Root RT index, if target is partitioned */
 	bool		partColsUpdated;	/* some part key in hierarchy updated */
 	List	   *resultRelations;	/* integer list of RT indexes */
+	Index	    mergeTargetRelation;	/* RT index of the merge target */
 	int			resultRelIndex; /* index of first resultRel in plan's list */
 	int			rootResultRelIndex; /* index of the partitioned table root */
 	List	   *plans;			/* plan(s) producing source data */
@@ -237,6 +239,8 @@ typedef struct ModifyTable
 	Node	   *onConflictWhere;	/* WHERE for ON CONFLICT UPDATE */
 	Index		exclRelRTI;		/* RTI of the EXCLUDED pseudo relation */
 	List	   *exclRelTlist;	/* tlist of the EXCLUDED pseudo relation */
+	List	   *mergeSourceTargetList;
+	List	   *mergeActionList;	/* actions for MERGE */
 } ModifyTable;
 
 struct PartitionPruneInfo;		/* forward reference to struct below */
diff --git a/src/include/nodes/relation.h b/src/include/nodes/relation.h
index 6fd24203dd..c21c90af0a 100644
--- a/src/include/nodes/relation.h
+++ b/src/include/nodes/relation.h
@@ -1704,7 +1704,7 @@ typedef struct LockRowsPath
 } LockRowsPath;
 
 /*
- * ModifyTablePath represents performing INSERT/UPDATE/DELETE modifications
+ * ModifyTablePath represents performing INSERT/UPDATE/DELETE/MERGE
  *
  * We represent most things that will be in the ModifyTable plan node
  * literally, except we have child Path(s) not Plan(s).  But analysis of the
@@ -1713,12 +1713,13 @@ typedef struct LockRowsPath
 typedef struct ModifyTablePath
 {
 	Path		path;
-	CmdType		operation;		/* INSERT, UPDATE, or DELETE */
+	CmdType		operation;		/* INSERT, UPDATE, DELETE or MERGE */
 	bool		canSetTag;		/* do we set the command tag/es_processed? */
 	Index		nominalRelation;	/* Parent RT index for use of EXPLAIN */
 	Index		rootRelation;	/* Root RT index, if target is partitioned */
 	bool		partColsUpdated;	/* some part key in hierarchy updated */
 	List	   *resultRelations;	/* integer list of RT indexes */
+	Index		mergeTargetRelation;	/* RT index of merge target relation */
 	List	   *subpaths;		/* Path(s) producing source data */
 	List	   *subroots;		/* per-target-table PlannerInfos */
 	List	   *withCheckOptionLists;	/* per-target-table WCO lists */
@@ -1726,6 +1727,8 @@ typedef struct ModifyTablePath
 	List	   *rowMarks;		/* PlanRowMarks (non-locking only) */
 	OnConflictExpr *onconflict; /* ON CONFLICT clause, or NULL */
 	int			epqParam;		/* ID of Param for EvalPlanQual re-eval */
+	List	   *mergeSourceTargetList;
+	List	   *mergeActionList;	/* actions for MERGE */
 } ModifyTablePath;
 
 /*
diff --git a/src/include/optimizer/pathnode.h b/src/include/optimizer/pathnode.h
index 81abcf53a8..20ec44a432 100644
--- a/src/include/optimizer/pathnode.h
+++ b/src/include/optimizer/pathnode.h
@@ -240,11 +240,14 @@ extern ModifyTablePath *create_modifytable_path(PlannerInfo *root,
 						CmdType operation, bool canSetTag,
 						Index nominalRelation, Index rootRelation,
 						bool partColsUpdated,
-						List *resultRelations, List *subpaths,
+						List *resultRelations,
+						Index	mergeTargetRelation,
+						List *subpaths,
 						List *subroots,
 						List *withCheckOptionLists, List *returningLists,
 						List *rowMarks, OnConflictExpr *onconflict,
-						int epqParam);
+						List *mergeSourceTargetList,
+						List *mergeActionList, int epqParam);
 extern LimitPath *create_limit_path(PlannerInfo *root, RelOptInfo *rel,
 				  Path *subpath,
 				  Node *limitOffset, Node *limitCount,
diff --git a/src/include/parser/analyze.h b/src/include/parser/analyze.h
index 7b5b90c4b3..23c6fcf657 100644
--- a/src/include/parser/analyze.h
+++ b/src/include/parser/analyze.h
@@ -32,6 +32,11 @@ extern Query *parse_sub_analyze(Node *parseTree, ParseState *parentParseState,
 				  bool locked_from_parent,
 				  bool resolve_unknowns);
 
+extern List *transformInsertRow(ParseState *pstate, List *exprlist,
+				   List *stmtcols, List *icolumns, List *attrnos,
+				   bool strip_indirection);
+extern List *transformUpdateTargetList(ParseState *pstate,
+						  List *targetList);
 extern Query *transformTopLevelStmt(ParseState *pstate, RawStmt *parseTree);
 extern Query *transformStmt(ParseState *pstate, Node *parseTree);
 
diff --git a/src/include/parser/kwlist.h b/src/include/parser/kwlist.h
index 23db40147b..81f758afbf 100644
--- a/src/include/parser/kwlist.h
+++ b/src/include/parser/kwlist.h
@@ -245,8 +245,10 @@ PG_KEYWORD("locked", LOCKED, UNRESERVED_KEYWORD)
 PG_KEYWORD("logged", LOGGED, UNRESERVED_KEYWORD)
 PG_KEYWORD("mapping", MAPPING, UNRESERVED_KEYWORD)
 PG_KEYWORD("match", MATCH, UNRESERVED_KEYWORD)
+PG_KEYWORD("matched", MATCHED, UNRESERVED_KEYWORD)
 PG_KEYWORD("materialized", MATERIALIZED, UNRESERVED_KEYWORD)
 PG_KEYWORD("maxvalue", MAXVALUE, UNRESERVED_KEYWORD)
+PG_KEYWORD("merge", MERGE, UNRESERVED_KEYWORD)
 PG_KEYWORD("method", METHOD, UNRESERVED_KEYWORD)
 PG_KEYWORD("minute", MINUTE_P, UNRESERVED_KEYWORD)
 PG_KEYWORD("minvalue", MINVALUE, UNRESERVED_KEYWORD)
diff --git a/src/include/parser/parse_clause.h b/src/include/parser/parse_clause.h
index f37f55302f..3e227d5790 100644
--- a/src/include/parser/parse_clause.h
+++ b/src/include/parser/parse_clause.h
@@ -19,7 +19,10 @@
 extern void transformFromClause(ParseState *pstate, List *frmList);
 extern int setTargetTable(ParseState *pstate, RangeVar *relation,
 			   bool inh, bool alsoSource, AclMode requiredPerms);
-
+extern Node *transformFromClauseItem(ParseState *pstate, Node *n,
+						RangeTblEntry **top_rte, int *top_rti,
+						RangeTblEntry **right_rte, int *right_rti,
+						List **fnamespace);
 extern Node *transformWhereClause(ParseState *pstate, Node *clause,
 					 ParseExprKind exprKind, const char *constructName);
 extern Node *transformLimitClause(ParseState *pstate, Node *clause,
diff --git a/src/include/parser/parse_merge.h b/src/include/parser/parse_merge.h
new file mode 100644
index 0000000000..0151809e09
--- /dev/null
+++ b/src/include/parser/parse_merge.h
@@ -0,0 +1,19 @@
+/*-------------------------------------------------------------------------
+ *
+ * parse_merge.h
+ *	  handle merge-stmt in parser
+ *
+ *
+ * Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/parser/parse_merge.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef PARSE_MERGE_H
+#define PARSE_MERGE_H
+
+#include "parser/parse_node.h"
+extern Query *transformMergeStmt(ParseState *pstate, MergeStmt *stmt);
+#endif
diff --git a/src/include/parser/parse_node.h b/src/include/parser/parse_node.h
index 0230543810..3fd2151ccb 100644
--- a/src/include/parser/parse_node.h
+++ b/src/include/parser/parse_node.h
@@ -50,6 +50,7 @@ typedef enum ParseExprKind
 	EXPR_KIND_INSERT_TARGET,	/* INSERT target list item */
 	EXPR_KIND_UPDATE_SOURCE,	/* UPDATE assignment source item */
 	EXPR_KIND_UPDATE_TARGET,	/* UPDATE assignment target item */
+	EXPR_KIND_MERGE_WHEN_AND,	/* MERGE WHEN ... AND condition */
 	EXPR_KIND_GROUP_BY,			/* GROUP BY */
 	EXPR_KIND_ORDER_BY,			/* ORDER BY */
 	EXPR_KIND_DISTINCT_ON,		/* DISTINCT ON */
@@ -127,7 +128,7 @@ typedef Node *(*CoerceParamHook) (ParseState *pstate, Param *param,
  * p_parent_cte: CommonTableExpr that immediately contains the current query,
  * if any.
  *
- * p_target_relation: target relation, if query is INSERT, UPDATE, or DELETE.
+ * p_target_relation: target relation, if query is INSERT/UPDATE/DELETE/MERGE
  *
  * p_target_rangetblentry: target relation's entry in the rtable list.
  *
@@ -181,7 +182,7 @@ struct ParseState
 	List	   *p_ctenamespace; /* current namespace for common table exprs */
 	List	   *p_future_ctes;	/* common table exprs not yet in namespace */
 	CommonTableExpr *p_parent_cte;	/* this query's containing CTE */
-	Relation	p_target_relation;	/* INSERT/UPDATE/DELETE target rel */
+	Relation	p_target_relation;	/* INSERT/UPDATE/DELETE/MERGE target rel */
 	RangeTblEntry *p_target_rangetblentry;	/* target rel's RTE */
 	bool		p_is_insert;	/* process assignment like INSERT not UPDATE */
 	List	   *p_windowdefs;	/* raw representations of window clauses */
diff --git a/src/include/rewrite/rewriteHandler.h b/src/include/rewrite/rewriteHandler.h
index 8128199fc3..1ab5de3942 100644
--- a/src/include/rewrite/rewriteHandler.h
+++ b/src/include/rewrite/rewriteHandler.h
@@ -25,6 +25,7 @@ extern void AcquireRewriteLocks(Query *parsetree,
 extern Node *build_column_default(Relation rel, int attrno);
 extern void rewriteTargetListUD(Query *parsetree, RangeTblEntry *target_rte,
 					Relation target_relation);
+extern void rewriteTargetListMerge(Query *parsetree, Relation target_relation);
 
 extern Query *get_view_query(Relation view);
 extern const char *view_query_is_auto_updatable(Query *viewquery,
diff --git a/src/interfaces/libpq/fe-exec.c b/src/interfaces/libpq/fe-exec.c
index 6aed8c87c7..ef62536996 100644
--- a/src/interfaces/libpq/fe-exec.c
+++ b/src/interfaces/libpq/fe-exec.c
@@ -3084,9 +3084,9 @@ PQoidValue(const PGresult *res)
 
 /*
  * PQcmdTuples -
- *	If the last command was INSERT/UPDATE/DELETE/MOVE/FETCH/COPY, return
- *	a string containing the number of inserted/affected tuples. If not,
- *	return "".
+ *	If the last command was INSERT/UPDATE/DELETE/MERGE/MOVE/FETCH/COPY,
+ *	return a string containing the number of inserted/affected tuples.
+ *	If not, return "".
  *
  *	XXX: this should probably return an int
  */
@@ -3113,7 +3113,8 @@ PQcmdTuples(PGresult *res)
 			 strncmp(res->cmdStatus, "DELETE ", 7) == 0 ||
 			 strncmp(res->cmdStatus, "UPDATE ", 7) == 0)
 		p = res->cmdStatus + 7;
-	else if (strncmp(res->cmdStatus, "FETCH ", 6) == 0)
+	else if (strncmp(res->cmdStatus, "FETCH ", 6) == 0 ||
+			 strncmp(res->cmdStatus, "MERGE ", 6) == 0)
 		p = res->cmdStatus + 6;
 	else if (strncmp(res->cmdStatus, "MOVE ", 5) == 0 ||
 			 strncmp(res->cmdStatus, "COPY ", 5) == 0)
diff --git a/src/pl/plpgsql/src/pl_exec.c b/src/pl/plpgsql/src/pl_exec.c
index 39ea925820..7f44befe76 100644
--- a/src/pl/plpgsql/src/pl_exec.c
+++ b/src/pl/plpgsql/src/pl_exec.c
@@ -4052,7 +4052,7 @@ exec_stmt_execsql(PLpgSQL_execstate *estate,
 
 	/*
 	 * On the first call for this statement generate the plan, and detect
-	 * whether the statement is INSERT/UPDATE/DELETE
+	 * whether the statement is INSERT/UPDATE/DELETE/MERGE
 	 */
 	if (expr->plan == NULL)
 	{
@@ -4073,7 +4073,8 @@ exec_stmt_execsql(PLpgSQL_execstate *estate,
 			if (plansource->commandTag &&
 				(strcmp(plansource->commandTag, "INSERT") == 0 ||
 				 strcmp(plansource->commandTag, "UPDATE") == 0 ||
-				 strcmp(plansource->commandTag, "DELETE") == 0))
+				 strcmp(plansource->commandTag, "DELETE") == 0 ||
+				 strcmp(plansource->commandTag, "MERGE") == 0))
 			{
 				stmt->mod_stmt = true;
 				break;
@@ -4132,6 +4133,7 @@ exec_stmt_execsql(PLpgSQL_execstate *estate,
 		case SPI_OK_INSERT_RETURNING:
 		case SPI_OK_UPDATE_RETURNING:
 		case SPI_OK_DELETE_RETURNING:
+		case SPI_OK_MERGE:
 			Assert(stmt->mod_stmt);
 			exec_set_found(estate, (SPI_processed != 0));
 			break;
@@ -4315,6 +4317,7 @@ exec_stmt_dynexecute(PLpgSQL_execstate *estate,
 		case SPI_OK_INSERT_RETURNING:
 		case SPI_OK_UPDATE_RETURNING:
 		case SPI_OK_DELETE_RETURNING:
+		case SPI_OK_MERGE:
 		case SPI_OK_UTILITY:
 		case SPI_OK_REWRITTEN:
 			break;
diff --git a/src/pl/plpgsql/src/pl_gram.y b/src/pl/plpgsql/src/pl_gram.y
index a979a5109d..85c8e2e2d8 100644
--- a/src/pl/plpgsql/src/pl_gram.y
+++ b/src/pl/plpgsql/src/pl_gram.y
@@ -304,6 +304,7 @@ static	void			check_raise_parameters(PLpgSQL_stmt_raise *stmt);
 %token <keyword>	K_LAST
 %token <keyword>	K_LOG
 %token <keyword>	K_LOOP
+%token <keyword>	K_MERGE
 %token <keyword>	K_MESSAGE
 %token <keyword>	K_MESSAGE_TEXT
 %token <keyword>	K_MOVE
@@ -1947,6 +1948,10 @@ stmt_execsql	: K_IMPORT
 					{
 						$$ = make_execsql_stmt(K_INSERT, @1);
 					}
+				| K_MERGE
+					{
+						$$ = make_execsql_stmt(K_MERGE, @1);
+					}
 				| T_WORD
 					{
 						int			tok;
@@ -2493,6 +2498,7 @@ unreserved_keyword	:
 				| K_IS
 				| K_LAST
 				| K_LOG
+				| K_MERGE
 				| K_MESSAGE
 				| K_MESSAGE_TEXT
 				| K_MOVE
@@ -2955,6 +2961,8 @@ make_execsql_stmt(int firsttoken, int location)
 		{
 			if (prev_tok == K_INSERT)
 				continue;		/* INSERT INTO is not an INTO-target */
+			if (prev_tok == K_MERGE)
+				continue;		/* MERGE INTO is not an INTO-target */
 			if (firsttoken == K_IMPORT)
 				continue;		/* IMPORT ... INTO is not an INTO-target */
 			if (have_into)
diff --git a/src/pl/plpgsql/src/pl_scanner.c b/src/pl/plpgsql/src/pl_scanner.c
index ab18946847..287fc9d901 100644
--- a/src/pl/plpgsql/src/pl_scanner.c
+++ b/src/pl/plpgsql/src/pl_scanner.c
@@ -138,6 +138,7 @@ static const ScanKeyword unreserved_keywords[] = {
 	PG_KEYWORD("is", K_IS, UNRESERVED_KEYWORD)
 	PG_KEYWORD("last", K_LAST, UNRESERVED_KEYWORD)
 	PG_KEYWORD("log", K_LOG, UNRESERVED_KEYWORD)
+	PG_KEYWORD("merge", K_MERGE, UNRESERVED_KEYWORD)
 	PG_KEYWORD("message", K_MESSAGE, UNRESERVED_KEYWORD)
 	PG_KEYWORD("message_text", K_MESSAGE_TEXT, UNRESERVED_KEYWORD)
 	PG_KEYWORD("move", K_MOVE, UNRESERVED_KEYWORD)
diff --git a/src/pl/plpgsql/src/plpgsql.h b/src/pl/plpgsql/src/plpgsql.h
index 42177ccaa6..be6f3ee8df 100644
--- a/src/pl/plpgsql/src/plpgsql.h
+++ b/src/pl/plpgsql/src/plpgsql.h
@@ -861,8 +861,8 @@ typedef struct PLpgSQL_stmt_execsql
 	PLpgSQL_stmt_type cmd_type;
 	int			lineno;
 	PLpgSQL_expr *sqlstmt;
-	bool		mod_stmt;		/* is the stmt INSERT/UPDATE/DELETE?  Note:
-								 * mod_stmt is set when we plan the query */
+	bool		mod_stmt;		/* is the stmt INSERT/UPDATE/DELETE/MERGE?
+								 * Note mod_stmt is set when we plan the query */
 	bool		into;			/* INTO supplied? */
 	bool		strict;			/* INTO STRICT flag */
 	PLpgSQL_variable *target;	/* INTO target (record or row) */
diff --git a/src/test/isolation/expected/merge-delete.out b/src/test/isolation/expected/merge-delete.out
new file mode 100644
index 0000000000..40e62901b7
--- /dev/null
+++ b/src/test/isolation/expected/merge-delete.out
@@ -0,0 +1,97 @@
+Parsed test spec with 2 sessions
+
+starting permutation: delete c1 select2 c2
+step delete: DELETE FROM target t WHERE t.key = 1;
+step c1: COMMIT;
+step select2: SELECT * FROM target;
+key            val            
+
+step c2: COMMIT;
+
+starting permutation: merge_delete c1 select2 c2
+step merge_delete: MERGE INTO target t USING (SELECT 1 as key) s ON s.key = t.key WHEN MATCHED THEN DELETE;
+step c1: COMMIT;
+step select2: SELECT * FROM target;
+key            val            
+
+step c2: COMMIT;
+
+starting permutation: delete c1 update1 select2 c2
+step delete: DELETE FROM target t WHERE t.key = 1;
+step c1: COMMIT;
+step update1: UPDATE target t SET val = t.val || ' updated by update1' WHERE t.key = 1;
+step select2: SELECT * FROM target;
+key            val            
+
+step c2: COMMIT;
+
+starting permutation: merge_delete c1 update1 select2 c2
+step merge_delete: MERGE INTO target t USING (SELECT 1 as key) s ON s.key = t.key WHEN MATCHED THEN DELETE;
+step c1: COMMIT;
+step update1: UPDATE target t SET val = t.val || ' updated by update1' WHERE t.key = 1;
+step select2: SELECT * FROM target;
+key            val            
+
+step c2: COMMIT;
+
+starting permutation: delete c1 merge2 select2 c2
+step delete: DELETE FROM target t WHERE t.key = 1;
+step c1: COMMIT;
+step merge2: MERGE INTO target t USING (SELECT 1 as key, 'merge2a' as val) s ON s.key = t.key WHEN NOT MATCHED THEN INSERT VALUES (s.key, s.val) WHEN MATCHED THEN UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+step select2: SELECT * FROM target;
+key            val            
+
+1              merge2a        
+step c2: COMMIT;
+
+starting permutation: merge_delete c1 merge2 select2 c2
+step merge_delete: MERGE INTO target t USING (SELECT 1 as key) s ON s.key = t.key WHEN MATCHED THEN DELETE;
+step c1: COMMIT;
+step merge2: MERGE INTO target t USING (SELECT 1 as key, 'merge2a' as val) s ON s.key = t.key WHEN NOT MATCHED THEN INSERT VALUES (s.key, s.val) WHEN MATCHED THEN UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+step select2: SELECT * FROM target;
+key            val            
+
+1              merge2a        
+step c2: COMMIT;
+
+starting permutation: delete update1 c1 select2 c2
+step delete: DELETE FROM target t WHERE t.key = 1;
+step update1: UPDATE target t SET val = t.val || ' updated by update1' WHERE t.key = 1; <waiting ...>
+step c1: COMMIT;
+step update1: <... completed>
+step select2: SELECT * FROM target;
+key            val            
+
+step c2: COMMIT;
+
+starting permutation: merge_delete update1 c1 select2 c2
+step merge_delete: MERGE INTO target t USING (SELECT 1 as key) s ON s.key = t.key WHEN MATCHED THEN DELETE;
+step update1: UPDATE target t SET val = t.val || ' updated by update1' WHERE t.key = 1; <waiting ...>
+step c1: COMMIT;
+step update1: <... completed>
+step select2: SELECT * FROM target;
+key            val            
+
+step c2: COMMIT;
+
+starting permutation: delete merge2 c1 select2 c2
+step delete: DELETE FROM target t WHERE t.key = 1;
+step merge2: MERGE INTO target t USING (SELECT 1 as key, 'merge2a' as val) s ON s.key = t.key WHEN NOT MATCHED THEN INSERT VALUES (s.key, s.val) WHEN MATCHED THEN UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val; <waiting ...>
+step c1: COMMIT;
+step merge2: <... completed>
+step select2: SELECT * FROM target;
+key            val            
+
+1              merge2a        
+step c2: COMMIT;
+
+starting permutation: merge_delete merge2 c1 select2 c2
+step merge_delete: MERGE INTO target t USING (SELECT 1 as key) s ON s.key = t.key WHEN MATCHED THEN DELETE;
+step merge2: MERGE INTO target t USING (SELECT 1 as key, 'merge2a' as val) s ON s.key = t.key WHEN NOT MATCHED THEN INSERT VALUES (s.key, s.val) WHEN MATCHED THEN UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val; <waiting ...>
+step c1: COMMIT;
+step merge2: <... completed>
+step select2: SELECT * FROM target;
+key            val            
+
+1              merge2a        
+step c2: COMMIT;
diff --git a/src/test/isolation/expected/merge-insert-update.out b/src/test/isolation/expected/merge-insert-update.out
new file mode 100644
index 0000000000..317fa16a3d
--- /dev/null
+++ b/src/test/isolation/expected/merge-insert-update.out
@@ -0,0 +1,84 @@
+Parsed test spec with 2 sessions
+
+starting permutation: merge1 c1 select2 c2
+step merge1: MERGE INTO target t USING (SELECT 1 as key, 'merge1' as val) s ON s.key = t.key WHEN NOT MATCHED THEN INSERT VALUES (s.key, s.val) WHEN MATCHED THEN UPDATE set val = t.val || ' updated by merge1';
+step c1: COMMIT;
+step select2: SELECT * FROM target;
+key            val            
+
+1              merge1         
+step c2: COMMIT;
+
+starting permutation: merge1 c1 merge2 select2 c2
+step merge1: MERGE INTO target t USING (SELECT 1 as key, 'merge1' as val) s ON s.key = t.key WHEN NOT MATCHED THEN INSERT VALUES (s.key, s.val) WHEN MATCHED THEN UPDATE set val = t.val || ' updated by merge1';
+step c1: COMMIT;
+step merge2: MERGE INTO target t USING (SELECT 1 as key, 'merge2' as val) s ON s.key = t.key WHEN NOT MATCHED THEN INSERT VALUES (s.key, s.val) WHEN MATCHED THEN UPDATE set val = t.val || ' updated by merge2';
+step select2: SELECT * FROM target;
+key            val            
+
+1              merge1 updated by merge2
+step c2: COMMIT;
+
+starting permutation: insert1 merge2 c1 select2 c2
+step insert1: INSERT INTO target VALUES (1, 'insert1');
+step merge2: MERGE INTO target t USING (SELECT 1 as key, 'merge2' as val) s ON s.key = t.key WHEN NOT MATCHED THEN INSERT VALUES (s.key, s.val) WHEN MATCHED THEN UPDATE set val = t.val || ' updated by merge2'; <waiting ...>
+step c1: COMMIT;
+step merge2: <... completed>
+error in steps c1 merge2: ERROR:  duplicate key value violates unique constraint "target_pkey"
+step select2: SELECT * FROM target;
+ERROR:  current transaction is aborted, commands ignored until end of transaction block
+step c2: COMMIT;
+
+starting permutation: merge1 merge2 c1 select2 c2
+step merge1: MERGE INTO target t USING (SELECT 1 as key, 'merge1' as val) s ON s.key = t.key WHEN NOT MATCHED THEN INSERT VALUES (s.key, s.val) WHEN MATCHED THEN UPDATE set val = t.val || ' updated by merge1';
+step merge2: MERGE INTO target t USING (SELECT 1 as key, 'merge2' as val) s ON s.key = t.key WHEN NOT MATCHED THEN INSERT VALUES (s.key, s.val) WHEN MATCHED THEN UPDATE set val = t.val || ' updated by merge2'; <waiting ...>
+step c1: COMMIT;
+step merge2: <... completed>
+error in steps c1 merge2: ERROR:  duplicate key value violates unique constraint "target_pkey"
+step select2: SELECT * FROM target;
+ERROR:  current transaction is aborted, commands ignored until end of transaction block
+step c2: COMMIT;
+
+starting permutation: merge1 merge2 a1 select2 c2
+step merge1: MERGE INTO target t USING (SELECT 1 as key, 'merge1' as val) s ON s.key = t.key WHEN NOT MATCHED THEN INSERT VALUES (s.key, s.val) WHEN MATCHED THEN UPDATE set val = t.val || ' updated by merge1';
+step merge2: MERGE INTO target t USING (SELECT 1 as key, 'merge2' as val) s ON s.key = t.key WHEN NOT MATCHED THEN INSERT VALUES (s.key, s.val) WHEN MATCHED THEN UPDATE set val = t.val || ' updated by merge2'; <waiting ...>
+step a1: ABORT;
+step merge2: <... completed>
+step select2: SELECT * FROM target;
+key            val            
+
+1              merge2         
+step c2: COMMIT;
+
+starting permutation: delete1 insert1 c1 merge2 select2 c2
+step delete1: DELETE FROM target WHERE key = 1;
+step insert1: INSERT INTO target VALUES (1, 'insert1');
+step c1: COMMIT;
+step merge2: MERGE INTO target t USING (SELECT 1 as key, 'merge2' as val) s ON s.key = t.key WHEN NOT MATCHED THEN INSERT VALUES (s.key, s.val) WHEN MATCHED THEN UPDATE set val = t.val || ' updated by merge2';
+step select2: SELECT * FROM target;
+key            val            
+
+1              insert1 updated by merge2
+step c2: COMMIT;
+
+starting permutation: delete1 insert1 merge2 c1 select2 c2
+step delete1: DELETE FROM target WHERE key = 1;
+step insert1: INSERT INTO target VALUES (1, 'insert1');
+step merge2: MERGE INTO target t USING (SELECT 1 as key, 'merge2' as val) s ON s.key = t.key WHEN NOT MATCHED THEN INSERT VALUES (s.key, s.val) WHEN MATCHED THEN UPDATE set val = t.val || ' updated by merge2'; <waiting ...>
+step c1: COMMIT;
+step merge2: <... completed>
+error in steps c1 merge2: ERROR:  duplicate key value violates unique constraint "target_pkey"
+step select2: SELECT * FROM target;
+ERROR:  current transaction is aborted, commands ignored until end of transaction block
+step c2: COMMIT;
+
+starting permutation: delete1 insert1 merge2i c1 select2 c2
+step delete1: DELETE FROM target WHERE key = 1;
+step insert1: INSERT INTO target VALUES (1, 'insert1');
+step merge2i: MERGE INTO target t USING (SELECT 1 as key, 'merge2' as val) s ON s.key = t.key WHEN MATCHED THEN UPDATE set val = t.val || ' updated by merge2';
+step c1: COMMIT;
+step select2: SELECT * FROM target;
+key            val            
+
+1              insert1        
+step c2: COMMIT;
diff --git a/src/test/isolation/expected/merge-match-recheck.out b/src/test/isolation/expected/merge-match-recheck.out
new file mode 100644
index 0000000000..96a9f45ac8
--- /dev/null
+++ b/src/test/isolation/expected/merge-match-recheck.out
@@ -0,0 +1,106 @@
+Parsed test spec with 2 sessions
+
+starting permutation: update1 merge_status c2 select1 c1
+step update1: UPDATE target t SET balance = balance + 10, val = t.val || ' updated by update1' WHERE t.key = 1;
+step merge_status: 
+  MERGE INTO target t
+  USING (SELECT 1 as key) s
+  ON s.key = t.key
+  WHEN MATCHED AND status = 's1' THEN
+	UPDATE SET status = 's2', val = t.val || ' when1'
+  WHEN MATCHED AND status = 's2' THEN
+	UPDATE SET status = 's3', val = t.val || ' when2'
+  WHEN MATCHED AND status = 's3' THEN
+	UPDATE SET status = 's4', val = t.val || ' when3';
+ <waiting ...>
+step c2: COMMIT;
+step merge_status: <... completed>
+step select1: SELECT * FROM target;
+key            balance        status         val            
+
+1              170            s2             setup updated by update1 when1
+step c1: COMMIT;
+
+starting permutation: update2 merge_status c2 select1 c1
+step update2: UPDATE target t SET status = 's2', val = t.val || ' updated by update2' WHERE t.key = 1;
+step merge_status: 
+  MERGE INTO target t
+  USING (SELECT 1 as key) s
+  ON s.key = t.key
+  WHEN MATCHED AND status = 's1' THEN
+	UPDATE SET status = 's2', val = t.val || ' when1'
+  WHEN MATCHED AND status = 's2' THEN
+	UPDATE SET status = 's3', val = t.val || ' when2'
+  WHEN MATCHED AND status = 's3' THEN
+	UPDATE SET status = 's4', val = t.val || ' when3';
+ <waiting ...>
+step c2: COMMIT;
+step merge_status: <... completed>
+step select1: SELECT * FROM target;
+key            balance        status         val            
+
+1              160            s3             setup updated by update2 when2
+step c1: COMMIT;
+
+starting permutation: update3 merge_status c2 select1 c1
+step update3: UPDATE target t SET status = 's3', val = t.val || ' updated by update3' WHERE t.key = 1;
+step merge_status: 
+  MERGE INTO target t
+  USING (SELECT 1 as key) s
+  ON s.key = t.key
+  WHEN MATCHED AND status = 's1' THEN
+	UPDATE SET status = 's2', val = t.val || ' when1'
+  WHEN MATCHED AND status = 's2' THEN
+	UPDATE SET status = 's3', val = t.val || ' when2'
+  WHEN MATCHED AND status = 's3' THEN
+	UPDATE SET status = 's4', val = t.val || ' when3';
+ <waiting ...>
+step c2: COMMIT;
+step merge_status: <... completed>
+step select1: SELECT * FROM target;
+key            balance        status         val            
+
+1              160            s4             setup updated by update3 when3
+step c1: COMMIT;
+
+starting permutation: update5 merge_status c2 select1 c1
+step update5: UPDATE target t SET status = 's5', val = t.val || ' updated by update5' WHERE t.key = 1;
+step merge_status: 
+  MERGE INTO target t
+  USING (SELECT 1 as key) s
+  ON s.key = t.key
+  WHEN MATCHED AND status = 's1' THEN
+	UPDATE SET status = 's2', val = t.val || ' when1'
+  WHEN MATCHED AND status = 's2' THEN
+	UPDATE SET status = 's3', val = t.val || ' when2'
+  WHEN MATCHED AND status = 's3' THEN
+	UPDATE SET status = 's4', val = t.val || ' when3';
+ <waiting ...>
+step c2: COMMIT;
+step merge_status: <... completed>
+step select1: SELECT * FROM target;
+key            balance        status         val            
+
+1              160            s5             setup updated by update5
+step c1: COMMIT;
+
+starting permutation: update_bal1 merge_bal c2 select1 c1
+step update_bal1: UPDATE target t SET balance = 50, val = t.val || ' updated by update_bal1' WHERE t.key = 1;
+step merge_bal: 
+  MERGE INTO target t
+  USING (SELECT 1 as key) s
+  ON s.key = t.key
+  WHEN MATCHED AND balance < 100 THEN
+	UPDATE SET balance = balance * 2, val = t.val || ' when1'
+  WHEN MATCHED AND balance < 200 THEN
+	UPDATE SET balance = balance * 4, val = t.val || ' when2'
+  WHEN MATCHED AND balance < 300 THEN
+	UPDATE SET balance = balance * 8, val = t.val || ' when3';
+ <waiting ...>
+step c2: COMMIT;
+step merge_bal: <... completed>
+step select1: SELECT * FROM target;
+key            balance        status         val            
+
+1              100            s1             setup updated by update_bal1 when1
+step c1: COMMIT;
diff --git a/src/test/isolation/expected/merge-update.out b/src/test/isolation/expected/merge-update.out
new file mode 100644
index 0000000000..68207a6f0e
--- /dev/null
+++ b/src/test/isolation/expected/merge-update.out
@@ -0,0 +1,238 @@
+Parsed test spec with 2 sessions
+
+starting permutation: merge1 c1 select2 c2
+step merge1: 
+  MERGE INTO target t
+  USING (SELECT 1 as key, 'merge1' as val) s
+  ON s.key = t.key
+  WHEN NOT MATCHED THEN
+	INSERT VALUES (s.key, s.val)
+  WHEN MATCHED THEN
+    UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+
+step c1: COMMIT;
+step select2: SELECT * FROM target;
+key            val            
+
+2              setup1 updated by merge1
+step c2: COMMIT;
+
+starting permutation: merge1 c1 merge2a select2 c2
+step merge1: 
+  MERGE INTO target t
+  USING (SELECT 1 as key, 'merge1' as val) s
+  ON s.key = t.key
+  WHEN NOT MATCHED THEN
+	INSERT VALUES (s.key, s.val)
+  WHEN MATCHED THEN
+    UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+
+step c1: COMMIT;
+step merge2a: 
+  MERGE INTO target t
+  USING (SELECT 1 as key, 'merge2a' as val) s
+  ON s.key = t.key
+  WHEN NOT MATCHED THEN
+	INSERT VALUES (s.key, s.val)
+  WHEN MATCHED THEN
+	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+
+step select2: SELECT * FROM target;
+key            val            
+
+2              setup1 updated by merge1
+1              merge2a        
+step c2: COMMIT;
+
+starting permutation: merge1 merge2a c1 select2 c2
+step merge1: 
+  MERGE INTO target t
+  USING (SELECT 1 as key, 'merge1' as val) s
+  ON s.key = t.key
+  WHEN NOT MATCHED THEN
+	INSERT VALUES (s.key, s.val)
+  WHEN MATCHED THEN
+    UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+
+step merge2a: 
+  MERGE INTO target t
+  USING (SELECT 1 as key, 'merge2a' as val) s
+  ON s.key = t.key
+  WHEN NOT MATCHED THEN
+	INSERT VALUES (s.key, s.val)
+  WHEN MATCHED THEN
+	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+ <waiting ...>
+step c1: COMMIT;
+step merge2a: <... completed>
+step select2: SELECT * FROM target;
+key            val            
+
+2              setup1 updated by merge1
+1              merge2a        
+step c2: COMMIT;
+
+starting permutation: merge1 merge2a a1 select2 c2
+step merge1: 
+  MERGE INTO target t
+  USING (SELECT 1 as key, 'merge1' as val) s
+  ON s.key = t.key
+  WHEN NOT MATCHED THEN
+	INSERT VALUES (s.key, s.val)
+  WHEN MATCHED THEN
+    UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+
+step merge2a: 
+  MERGE INTO target t
+  USING (SELECT 1 as key, 'merge2a' as val) s
+  ON s.key = t.key
+  WHEN NOT MATCHED THEN
+	INSERT VALUES (s.key, s.val)
+  WHEN MATCHED THEN
+	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+ <waiting ...>
+step a1: ABORT;
+step merge2a: <... completed>
+step select2: SELECT * FROM target;
+key            val            
+
+2              setup1 updated by merge2a
+step c2: COMMIT;
+
+starting permutation: merge1 merge2b c1 select2 c2
+step merge1: 
+  MERGE INTO target t
+  USING (SELECT 1 as key, 'merge1' as val) s
+  ON s.key = t.key
+  WHEN NOT MATCHED THEN
+	INSERT VALUES (s.key, s.val)
+  WHEN MATCHED THEN
+    UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+
+step merge2b: 
+  MERGE INTO target t
+  USING (SELECT 1 as key, 'merge2b' as val) s
+  ON s.key = t.key
+  WHEN NOT MATCHED THEN
+	INSERT VALUES (s.key, s.val)
+  WHEN MATCHED AND t.key < 2 THEN
+	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+ <waiting ...>
+step c1: COMMIT;
+step merge2b: <... completed>
+step select2: SELECT * FROM target;
+key            val            
+
+2              setup1 updated by merge1
+1              merge2b        
+step c2: COMMIT;
+
+starting permutation: merge1 merge2c c1 select2 c2
+step merge1: 
+  MERGE INTO target t
+  USING (SELECT 1 as key, 'merge1' as val) s
+  ON s.key = t.key
+  WHEN NOT MATCHED THEN
+	INSERT VALUES (s.key, s.val)
+  WHEN MATCHED THEN
+    UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+
+step merge2c: 
+  MERGE INTO target t
+  USING (SELECT 1 as key, 'merge2c' as val) s
+  ON s.key = t.key AND t.key < 2
+  WHEN NOT MATCHED THEN
+	INSERT VALUES (s.key, s.val)
+  WHEN MATCHED THEN
+	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+ <waiting ...>
+step c1: COMMIT;
+step merge2c: <... completed>
+step select2: SELECT * FROM target;
+key            val            
+
+2              setup1 updated by merge1
+1              merge2c        
+step c2: COMMIT;
+
+starting permutation: pa_merge1 pa_merge2a c1 pa_select2 c2
+step pa_merge1: 
+  MERGE INTO pa_target t
+  USING (SELECT 1 as key, 'pa_merge1' as val) s
+  ON s.key = t.key
+  WHEN NOT MATCHED THEN
+	INSERT VALUES (s.key, s.val)
+  WHEN MATCHED THEN
+    UPDATE set val = t.val || ' updated by ' || s.val;
+
+step pa_merge2a: 
+  MERGE INTO pa_target t
+  USING (SELECT 1 as key, 'pa_merge2a' as val) s
+  ON s.key = t.key
+  WHEN NOT MATCHED THEN
+	INSERT VALUES (s.key, s.val)
+  WHEN MATCHED THEN
+	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+ <waiting ...>
+step c1: COMMIT;
+step pa_merge2a: <... completed>
+step pa_select2: SELECT * FROM pa_target;
+key            val            
+
+2              initial        
+2              initial updated by pa_merge1 updated by pa_merge2a
+step c2: COMMIT;
+
+starting permutation: pa_merge2 pa_merge2a c1 pa_select2 c2
+step pa_merge2: 
+  MERGE INTO pa_target t
+  USING (SELECT 1 as key, 'pa_merge1' as val) s
+  ON s.key = t.key
+  WHEN NOT MATCHED THEN
+	INSERT VALUES (s.key, s.val)
+  WHEN MATCHED THEN
+    UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+
+step pa_merge2a: 
+  MERGE INTO pa_target t
+  USING (SELECT 1 as key, 'pa_merge2a' as val) s
+  ON s.key = t.key
+  WHEN NOT MATCHED THEN
+	INSERT VALUES (s.key, s.val)
+  WHEN MATCHED THEN
+	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+ <waiting ...>
+step c1: COMMIT;
+step pa_merge2a: <... completed>
+error in steps c1 pa_merge2a: ERROR:  tuple to be deleted was already moved to another partition due to concurrent update
+step pa_select2: SELECT * FROM pa_target;
+ERROR:  current transaction is aborted, commands ignored until end of transaction block
+step c2: COMMIT;
+
+starting permutation: pa_merge2 c1 pa_merge2a pa_select2 c2
+step pa_merge2: 
+  MERGE INTO pa_target t
+  USING (SELECT 1 as key, 'pa_merge1' as val) s
+  ON s.key = t.key
+  WHEN NOT MATCHED THEN
+	INSERT VALUES (s.key, s.val)
+  WHEN MATCHED THEN
+    UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+
+step c1: COMMIT;
+step pa_merge2a: 
+  MERGE INTO pa_target t
+  USING (SELECT 1 as key, 'pa_merge2a' as val) s
+  ON s.key = t.key
+  WHEN NOT MATCHED THEN
+	INSERT VALUES (s.key, s.val)
+  WHEN MATCHED THEN
+	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+
+step pa_select2: SELECT * FROM pa_target;
+key            val            
+
+1              pa_merge2a     
+2              initial        
+2              initial updated by pa_merge1
+step c2: COMMIT;
diff --git a/src/test/isolation/isolation_schedule b/src/test/isolation/isolation_schedule
index dd57a96e78..b8cb19faa4 100644
--- a/src/test/isolation/isolation_schedule
+++ b/src/test/isolation/isolation_schedule
@@ -33,6 +33,10 @@ test: insert-conflict-do-update
 test: insert-conflict-do-update-2
 test: insert-conflict-do-update-3
 test: insert-conflict-toast
+test: merge-insert-update
+test: merge-delete
+test: merge-update
+test: merge-match-recheck
 test: delete-abort-savept
 test: delete-abort-savept-2
 test: aborted-keyrevoke
diff --git a/src/test/isolation/specs/merge-delete.spec b/src/test/isolation/specs/merge-delete.spec
new file mode 100644
index 0000000000..656954f847
--- /dev/null
+++ b/src/test/isolation/specs/merge-delete.spec
@@ -0,0 +1,51 @@
+# MERGE DELETE
+#
+# This test looks at the interactions involving concurrent deletes
+# comparing the behavior of MERGE, DELETE and UPDATE
+
+setup
+{
+  CREATE TABLE target (key int primary key, val text);
+  INSERT INTO target VALUES (1, 'setup1');
+}
+
+teardown
+{
+  DROP TABLE target;
+}
+
+session "s1"
+setup
+{
+  BEGIN ISOLATION LEVEL READ COMMITTED;
+}
+step "delete" { DELETE FROM target t WHERE t.key = 1; }
+step "merge_delete" { MERGE INTO target t USING (SELECT 1 as key) s ON s.key = t.key WHEN MATCHED THEN DELETE; }
+step "c1" { COMMIT; }
+step "a1" { ABORT; }
+
+session "s2"
+setup
+{
+  BEGIN ISOLATION LEVEL READ COMMITTED;
+}
+step "update1" { UPDATE target t SET val = t.val || ' updated by update1' WHERE t.key = 1; }
+step "merge2" { MERGE INTO target t USING (SELECT 1 as key, 'merge2a' as val) s ON s.key = t.key WHEN NOT MATCHED THEN INSERT VALUES (s.key, s.val) WHEN MATCHED THEN UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val; }
+step "select2" { SELECT * FROM target; }
+step "c2" { COMMIT; }
+
+# Basic effects
+permutation "delete" "c1" "select2" "c2"
+permutation "merge_delete" "c1" "select2" "c2"
+
+# One after the other, no concurrency
+permutation "delete" "c1" "update1" "select2" "c2"
+permutation "merge_delete" "c1" "update1" "select2" "c2"
+permutation "delete" "c1" "merge2" "select2" "c2"
+permutation "merge_delete" "c1" "merge2" "select2" "c2"
+
+# Now with concurrency
+permutation "delete" "update1" "c1" "select2" "c2"
+permutation "merge_delete" "update1" "c1" "select2" "c2"
+permutation "delete" "merge2" "c1" "select2" "c2"
+permutation "merge_delete" "merge2" "c1" "select2" "c2"
diff --git a/src/test/isolation/specs/merge-insert-update.spec b/src/test/isolation/specs/merge-insert-update.spec
new file mode 100644
index 0000000000..704492be1f
--- /dev/null
+++ b/src/test/isolation/specs/merge-insert-update.spec
@@ -0,0 +1,52 @@
+# MERGE INSERT UPDATE
+#
+# This looks at how we handle concurrent INSERTs, illustrating how the
+# behavior differs from INSERT ... ON CONFLICT
+
+setup
+{
+  CREATE TABLE target (key int primary key, val text);
+}
+
+teardown
+{
+  DROP TABLE target;
+}
+
+session "s1"
+setup
+{
+  BEGIN ISOLATION LEVEL READ COMMITTED;
+}
+step "merge1" { MERGE INTO target t USING (SELECT 1 as key, 'merge1' as val) s ON s.key = t.key WHEN NOT MATCHED THEN INSERT VALUES (s.key, s.val) WHEN MATCHED THEN UPDATE set val = t.val || ' updated by merge1'; }
+step "delete1" { DELETE FROM target WHERE key = 1; }
+step "insert1" { INSERT INTO target VALUES (1, 'insert1'); }
+step "c1" { COMMIT; }
+step "a1" { ABORT; }
+
+session "s2"
+setup
+{
+  BEGIN ISOLATION LEVEL READ COMMITTED;
+}
+step "merge2" { MERGE INTO target t USING (SELECT 1 as key, 'merge2' as val) s ON s.key = t.key WHEN NOT MATCHED THEN INSERT VALUES (s.key, s.val) WHEN MATCHED THEN UPDATE set val = t.val || ' updated by merge2'; }
+
+step "merge2i" { MERGE INTO target t USING (SELECT 1 as key, 'merge2' as val) s ON s.key = t.key WHEN MATCHED THEN UPDATE set val = t.val || ' updated by merge2'; }
+
+step "select2" { SELECT * FROM target; }
+step "c2" { COMMIT; }
+step "a2" { ABORT; }
+
+# Basic effects
+permutation "merge1" "c1" "select2" "c2"
+permutation "merge1" "c1" "merge2" "select2" "c2"
+
+# check concurrent inserts
+permutation "insert1" "merge2" "c1" "select2" "c2"
+permutation "merge1" "merge2" "c1" "select2" "c2"
+permutation "merge1" "merge2" "a1" "select2" "c2"
+
+# check how we handle when visible row has been concurrently deleted, then same key re-inserted
+permutation "delete1" "insert1" "c1" "merge2" "select2" "c2"
+permutation "delete1" "insert1" "merge2" "c1" "select2" "c2"
+permutation "delete1" "insert1" "merge2i" "c1" "select2" "c2"
diff --git a/src/test/isolation/specs/merge-match-recheck.spec b/src/test/isolation/specs/merge-match-recheck.spec
new file mode 100644
index 0000000000..193033da17
--- /dev/null
+++ b/src/test/isolation/specs/merge-match-recheck.spec
@@ -0,0 +1,79 @@
+# MERGE MATCHED RECHECK
+#
+# This test looks at what happens when we have complex
+# WHEN MATCHED AND conditions and a concurrent UPDATE causes a
+# recheck of the AND condition on the new row
+
+setup
+{
+  CREATE TABLE target (key int primary key, balance integer, status text, val text);
+  INSERT INTO target VALUES (1, 160, 's1', 'setup');
+}
+
+teardown
+{
+  DROP TABLE target;
+}
+
+session "s1"
+setup
+{
+  BEGIN ISOLATION LEVEL READ COMMITTED;
+}
+step "merge_status"
+{
+  MERGE INTO target t
+  USING (SELECT 1 as key) s
+  ON s.key = t.key
+  WHEN MATCHED AND status = 's1' THEN
+	UPDATE SET status = 's2', val = t.val || ' when1'
+  WHEN MATCHED AND status = 's2' THEN
+	UPDATE SET status = 's3', val = t.val || ' when2'
+  WHEN MATCHED AND status = 's3' THEN
+	UPDATE SET status = 's4', val = t.val || ' when3';
+}
+
+step "merge_bal"
+{
+  MERGE INTO target t
+  USING (SELECT 1 as key) s
+  ON s.key = t.key
+  WHEN MATCHED AND balance < 100 THEN
+	UPDATE SET balance = balance * 2, val = t.val || ' when1'
+  WHEN MATCHED AND balance < 200 THEN
+	UPDATE SET balance = balance * 4, val = t.val || ' when2'
+  WHEN MATCHED AND balance < 300 THEN
+	UPDATE SET balance = balance * 8, val = t.val || ' when3';
+}
+
+step "select1" { SELECT * FROM target; }
+step "c1" { COMMIT; }
+step "a1" { ABORT; }
+
+session "s2"
+setup
+{
+  BEGIN ISOLATION LEVEL READ COMMITTED;
+}
+step "update1" { UPDATE target t SET balance = balance + 10, val = t.val || ' updated by update1' WHERE t.key = 1; }
+step "update2" { UPDATE target t SET status = 's2', val = t.val || ' updated by update2' WHERE t.key = 1; }
+step "update3" { UPDATE target t SET status = 's3', val = t.val || ' updated by update3' WHERE t.key = 1; }
+step "update5" { UPDATE target t SET status = 's5', val = t.val || ' updated by update5' WHERE t.key = 1; }
+step "update_bal1" { UPDATE target t SET balance = 50, val = t.val || ' updated by update_bal1' WHERE t.key = 1; }
+step "select2" { SELECT * FROM target; }
+step "c2" { COMMIT; }
+
+# merge_status sees concurrently updated row and rechecks WHEN conditions, but recheck passes and final status = 's2'
+permutation "update1" "merge_status" "c2" "select1" "c1"
+
+# merge_status sees concurrently updated row and rechecks WHEN conditions, recheck fails, so final status = 's3' not 's2'
+permutation "update2" "merge_status" "c2" "select1" "c1"
+
+# merge_status sees concurrently updated row and rechecks WHEN conditions, recheck fails, so final status = 's4' not 's2'
+permutation "update3" "merge_status" "c2" "select1" "c1"
+
+# merge_status sees concurrently updated row and rechecks WHEN conditions, recheck fails, but we skip update and MERGE does nothing
+permutation "update5" "merge_status" "c2" "select1" "c1"
+
+# merge_bal sees concurrently updated row and rechecks WHEN conditions, recheck fails, so final balance = 100 not 640
+permutation "update_bal1" "merge_bal" "c2" "select1" "c1"
diff --git a/src/test/isolation/specs/merge-update.spec b/src/test/isolation/specs/merge-update.spec
new file mode 100644
index 0000000000..625b477eb9
--- /dev/null
+++ b/src/test/isolation/specs/merge-update.spec
@@ -0,0 +1,133 @@
+# MERGE UPDATE
+#
+# This test exercises atypical cases
+# 1. UPDATEs of PKs that change the join in the ON clause
+# 2. UPDATEs with WHEN AND conditions that would fail after concurrent update
+# 3. UPDATEs with extra ON conditions that would fail after concurrent update
+
+setup
+{
+  CREATE TABLE target (key int primary key, val text);
+  INSERT INTO target VALUES (1, 'setup1');
+
+  CREATE TABLE pa_target (key integer, val text)
+	  PARTITION BY LIST (key);
+  CREATE TABLE part1 (key integer, val text);
+  CREATE TABLE part2 (val text, key integer);
+  CREATE TABLE part3 (key integer, val text);
+
+  ALTER TABLE pa_target ATTACH PARTITION part1 FOR VALUES IN (1,4);
+  ALTER TABLE pa_target ATTACH PARTITION part2 FOR VALUES IN (2,5,6);
+  ALTER TABLE pa_target ATTACH PARTITION part3 DEFAULT;
+
+  INSERT INTO pa_target VALUES (1, 'initial');
+  INSERT INTO pa_target VALUES (2, 'initial');
+}
+
+teardown
+{
+  DROP TABLE target;
+  DROP TABLE pa_target CASCADE;
+}
+
+session "s1"
+setup
+{
+  BEGIN ISOLATION LEVEL READ COMMITTED;
+}
+step "merge1"
+{
+  MERGE INTO target t
+  USING (SELECT 1 as key, 'merge1' as val) s
+  ON s.key = t.key
+  WHEN NOT MATCHED THEN
+	INSERT VALUES (s.key, s.val)
+  WHEN MATCHED THEN
+    UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+}
+step "pa_merge1"
+{
+  MERGE INTO pa_target t
+  USING (SELECT 1 as key, 'pa_merge1' as val) s
+  ON s.key = t.key
+  WHEN NOT MATCHED THEN
+	INSERT VALUES (s.key, s.val)
+  WHEN MATCHED THEN
+    UPDATE set val = t.val || ' updated by ' || s.val;
+}
+step "pa_merge2"
+{
+  MERGE INTO pa_target t
+  USING (SELECT 1 as key, 'pa_merge1' as val) s
+  ON s.key = t.key
+  WHEN NOT MATCHED THEN
+	INSERT VALUES (s.key, s.val)
+  WHEN MATCHED THEN
+    UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+}
+step "c1" { COMMIT; }
+step "a1" { ABORT; }
+
+session "s2"
+setup
+{
+  BEGIN ISOLATION LEVEL READ COMMITTED;
+}
+step "merge2a"
+{
+  MERGE INTO target t
+  USING (SELECT 1 as key, 'merge2a' as val) s
+  ON s.key = t.key
+  WHEN NOT MATCHED THEN
+	INSERT VALUES (s.key, s.val)
+  WHEN MATCHED THEN
+	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+}
+step "merge2b"
+{
+  MERGE INTO target t
+  USING (SELECT 1 as key, 'merge2b' as val) s
+  ON s.key = t.key
+  WHEN NOT MATCHED THEN
+	INSERT VALUES (s.key, s.val)
+  WHEN MATCHED AND t.key < 2 THEN
+	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+}
+step "merge2c"
+{
+  MERGE INTO target t
+  USING (SELECT 1 as key, 'merge2c' as val) s
+  ON s.key = t.key AND t.key < 2
+  WHEN NOT MATCHED THEN
+	INSERT VALUES (s.key, s.val)
+  WHEN MATCHED THEN
+	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+}
+step "pa_merge2a"
+{
+  MERGE INTO pa_target t
+  USING (SELECT 1 as key, 'pa_merge2a' as val) s
+  ON s.key = t.key
+  WHEN NOT MATCHED THEN
+	INSERT VALUES (s.key, s.val)
+  WHEN MATCHED THEN
+	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+}
+step "select2" { SELECT * FROM target; }
+step "pa_select2" { SELECT * FROM pa_target; }
+step "c2" { COMMIT; }
+
+# Basic effects
+permutation "merge1" "c1" "select2" "c2"
+
+# One after the other, no concurrency
+permutation "merge1" "c1" "merge2a" "select2" "c2"
+
+# Now with concurrency
+permutation "merge1" "merge2a" "c1" "select2" "c2"
+permutation "merge1" "merge2a" "a1" "select2" "c2"
+permutation "merge1" "merge2b" "c1" "select2" "c2"
+permutation "merge1" "merge2c" "c1" "select2" "c2"
+permutation "pa_merge1" "pa_merge2a" "c1" "pa_select2" "c2"
+permutation "pa_merge2" "pa_merge2a" "c1" "pa_select2" "c2" # fails
+permutation "pa_merge2" "c1" "pa_merge2a" "pa_select2" "c2" # succeeds
diff --git a/src/test/regress/expected/identity.out b/src/test/regress/expected/identity.out
index d7d5178f5d..3a6016c80a 100644
--- a/src/test/regress/expected/identity.out
+++ b/src/test/regress/expected/identity.out
@@ -386,3 +386,58 @@ CREATE TABLE itest_child PARTITION OF itest_parent (
 ) FOR VALUES FROM ('2016-07-01') TO ('2016-08-01'); -- error
 ERROR:  identity columns are not supported on partitions
 DROP TABLE itest_parent;
+-- MERGE tests
+CREATE TABLE itest14 (a int GENERATED ALWAYS AS IDENTITY, b text);
+CREATE TABLE itest15 (a int GENERATED BY DEFAULT AS IDENTITY, b text);
+MERGE INTO itest14 t
+USING (SELECT 10 AS s_a, 'inserted by merge' AS s_b) s
+ON t.a = s.s_a
+WHEN NOT MATCHED THEN
+	INSERT (a, b) VALUES (s.s_a, s.s_b);
+ERROR:  cannot insert into column "a"
+DETAIL:  Column "a" is an identity column defined as GENERATED ALWAYS.
+HINT:  Use OVERRIDING SYSTEM VALUE to override.
+MERGE INTO itest14 t
+USING (SELECT 20 AS s_a, 'inserted by merge' AS s_b) s
+ON t.a = s.s_a
+WHEN NOT MATCHED THEN
+	INSERT (a, b) OVERRIDING USER VALUE VALUES (s.s_a, s.s_b);
+ERROR:  cannot insert into column "a"
+DETAIL:  Column "a" is an identity column defined as GENERATED ALWAYS.
+HINT:  Use OVERRIDING SYSTEM VALUE to override.
+MERGE INTO itest14 t
+USING (SELECT 30 AS s_a, 'inserted by merge' AS s_b) s
+ON t.a = s.s_a
+WHEN NOT MATCHED THEN
+	INSERT (a, b) OVERRIDING SYSTEM VALUE VALUES (s.s_a, s.s_b);
+MERGE INTO itest15 t
+USING (SELECT 10 AS s_a, 'inserted by merge' AS s_b) s
+ON t.a = s.s_a
+WHEN NOT MATCHED THEN
+	INSERT (a, b) VALUES (s.s_a, s.s_b);
+MERGE INTO itest15 t
+USING (SELECT 20 AS s_a, 'inserted by merge' AS s_b) s
+ON t.a = s.s_a
+WHEN NOT MATCHED THEN
+	INSERT (a, b) OVERRIDING USER VALUE VALUES (s.s_a, s.s_b);
+MERGE INTO itest15 t
+USING (SELECT 30 AS s_a, 'inserted by merge' AS s_b) s
+ON t.a = s.s_a
+WHEN NOT MATCHED THEN
+	INSERT (a, b) OVERRIDING SYSTEM VALUE VALUES (s.s_a, s.s_b);
+SELECT * FROM itest14;
+ a  |         b         
+----+-------------------
+ 30 | inserted by merge
+(1 row)
+
+SELECT * FROM itest15;
+ a  |         b         
+----+-------------------
+ 10 | inserted by merge
+  1 | inserted by merge
+ 30 | inserted by merge
+(3 rows)
+
+DROP TABLE itest14;
+DROP TABLE itest15;
diff --git a/src/test/regress/expected/merge.out b/src/test/regress/expected/merge.out
new file mode 100644
index 0000000000..9ca4e92e7e
--- /dev/null
+++ b/src/test/regress/expected/merge.out
@@ -0,0 +1,1655 @@
+--
+-- MERGE
+--
+--\set VERBOSITY verbose
+--set debug_print_rewritten = true;
+--set debug_print_parse = true;
+--set debug_print_pretty = true;
+CREATE USER merge_privs;
+CREATE USER merge_no_privs;
+DROP TABLE IF EXISTS target;
+NOTICE:  table "target" does not exist, skipping
+DROP TABLE IF EXISTS source;
+NOTICE:  table "source" does not exist, skipping
+CREATE TABLE target (tid integer, balance integer);
+CREATE TABLE source (sid integer, delta integer); --no index
+INSERT INTO target VALUES (1, 10);
+INSERT INTO target VALUES (2, 20);
+INSERT INTO target VALUES (3, 30);
+SELECT t.ctid is not null as matched, t.*, s.* FROM source s FULL OUTER JOIN target t ON s.sid = t.tid ORDER BY t.tid, s.sid;
+ matched | tid | balance | sid | delta 
+---------+-----+---------+-----+-------
+ t       |   1 |      10 |     |      
+ t       |   2 |      20 |     |      
+ t       |   3 |      30 |     |      
+(3 rows)
+
+ALTER TABLE target OWNER TO merge_privs;
+ALTER TABLE source OWNER TO merge_privs;
+CREATE TABLE target2 (tid integer, balance integer);
+CREATE TABLE source2 (sid integer, delta integer);
+ALTER TABLE target2 OWNER TO merge_no_privs;
+ALTER TABLE source2 OWNER TO merge_no_privs;
+GRANT INSERT ON target TO merge_no_privs;
+SET SESSION AUTHORIZATION merge_privs;
+EXPLAIN (COSTS OFF)
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED THEN
+	DELETE
+;
+                QUERY PLAN                
+------------------------------------------
+ Merge on target t
+   ->  Merge Join
+         Merge Cond: (t_1.tid = s.sid)
+         ->  Sort
+               Sort Key: t_1.tid
+               ->  Seq Scan on target t_1
+         ->  Sort
+               Sort Key: s.sid
+               ->  Seq Scan on source s
+(9 rows)
+
+--
+-- Errors
+--
+MERGE INTO target t RANDOMWORD
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED THEN
+	UPDATE SET balance = 0
+;
+ERROR:  syntax error at or near "RANDOMWORD"
+LINE 1: MERGE INTO target t RANDOMWORD
+                            ^
+-- MATCHED/INSERT error
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED THEN
+	INSERT DEFAULT VALUES
+;
+ERROR:  syntax error at or near "INSERT"
+LINE 5:  INSERT DEFAULT VALUES
+         ^
+-- incorrectly specifying INTO target
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT INTO target DEFAULT VALUES
+;
+ERROR:  syntax error at or near "INTO"
+LINE 5:  INSERT INTO target DEFAULT VALUES
+                ^
+-- Multiple VALUES clause
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT VALUES (1,1), (2,2);
+ERROR:  syntax error at or near ","
+LINE 5:  INSERT VALUES (1,1), (2,2);
+                            ^
+;
+-- SELECT query for INSERT
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT SELECT (1, 1);
+ERROR:  syntax error at or near "SELECT"
+LINE 5:  INSERT SELECT (1, 1);
+                ^
+;
+-- NOT MATCHED/UPDATE
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	UPDATE SET balance = 0
+;
+ERROR:  syntax error at or near "UPDATE"
+LINE 5:  UPDATE SET balance = 0
+         ^
+-- UPDATE tablename
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED THEN
+	UPDATE target SET balance = 0
+;
+ERROR:  syntax error at or near "target"
+LINE 5:  UPDATE target SET balance = 0
+                ^
+-- unsupported relation types
+-- view
+CREATE VIEW tv AS SELECT * FROM target;
+MERGE INTO tv t
+USING source s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT DEFAULT VALUES;
+ERROR:  MERGE is not supported for this relation type
+DROP VIEW tv;
+-- materialized view
+CREATE MATERIALIZED VIEW mv AS SELECT * FROM target;
+MERGE INTO mv t
+USING source s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT DEFAULT VALUES;
+ERROR:  MERGE is not supported for this relation type
+DROP MATERIALIZED VIEW mv;
+-- inherited table
+CREATE TABLE inhp (tid int, balance int);
+CREATE TABLE child1() INHERITS (inhp);
+CREATE TABLE child2() INHERITS (child1);
+MERGE INTO inhp t
+USING source s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT DEFAULT VALUES;
+ERROR:  MERGE is not supported for relations with inheritance
+MERGE INTO child1 t
+USING source s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT DEFAULT VALUES;
+ERROR:  MERGE is not supported for relations with inheritance
+-- this should be ok
+MERGE INTO child2 t
+USING source s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT DEFAULT VALUES;
+DROP TABLE inhp, child1, child2;
+-- permissions
+MERGE INTO target
+USING source2
+ON target.tid = source2.sid
+WHEN MATCHED THEN
+	UPDATE SET balance = 0
+;
+ERROR:  permission denied for table source2
+GRANT INSERT ON target TO merge_no_privs;
+SET SESSION AUTHORIZATION merge_no_privs;
+MERGE INTO target
+USING source2
+ON target.tid = source2.sid
+WHEN MATCHED THEN
+	UPDATE SET balance = 0
+;
+ERROR:  permission denied for table target
+GRANT UPDATE ON target2 TO merge_privs;
+SET SESSION AUTHORIZATION merge_privs;
+MERGE INTO target2
+USING source
+ON target2.tid = source.sid
+WHEN MATCHED THEN
+	DELETE
+;
+ERROR:  permission denied for table target2
+MERGE INTO target2
+USING source
+ON target2.tid = source.sid
+WHEN NOT MATCHED THEN
+	INSERT DEFAULT VALUES
+;
+ERROR:  permission denied for table target2
+-- check if the target can be accessed from source relation subquery; we should
+-- not be able to do so
+MERGE INTO target t
+USING (SELECT * FROM source WHERE t.tid > sid) s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT DEFAULT VALUES
+;
+ERROR:  invalid reference to FROM-clause entry for table "t"
+LINE 2: USING (SELECT * FROM source WHERE t.tid > sid) s
+                                          ^
+HINT:  There is an entry for table "t", but it cannot be referenced from this part of the query.
+--
+-- initial tests
+--
+-- zero rows in source has no effect
+MERGE INTO target
+USING source
+ON target.tid = source.sid
+WHEN MATCHED THEN
+	UPDATE SET balance = 0
+;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED THEN
+	UPDATE SET balance = 0
+;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED THEN
+	DELETE
+;
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT DEFAULT VALUES
+;
+ROLLBACK;
+-- insert some non-matching source rows to work from
+INSERT INTO source VALUES (4, 40);
+SELECT * FROM source ORDER BY sid;
+ sid | delta 
+-----+-------
+   4 |    40
+(1 row)
+
+SELECT * FROM target ORDER BY tid;
+ tid | balance 
+-----+---------
+   1 |      10
+   2 |      20
+   3 |      30
+(3 rows)
+
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	DO NOTHING
+;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED THEN
+	UPDATE SET balance = 0
+;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED THEN
+	DELETE
+;
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT DEFAULT VALUES
+;
+SELECT * FROM target ORDER BY tid;
+ tid | balance 
+-----+---------
+   1 |      10
+   2 |      20
+   3 |      30
+     |        
+(4 rows)
+
+ROLLBACK;
+-- index plans
+INSERT INTO target SELECT generate_series(1000,2500), 0;
+ALTER TABLE target ADD PRIMARY KEY (tid);
+ANALYZE target;
+EXPLAIN (COSTS OFF)
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED THEN
+	UPDATE SET balance = 0
+;
+                QUERY PLAN                
+------------------------------------------
+ Merge on target t
+   ->  Hash Join
+         Hash Cond: (s.sid = t_1.tid)
+         ->  Seq Scan on source s
+         ->  Hash
+               ->  Seq Scan on target t_1
+(6 rows)
+
+EXPLAIN (COSTS OFF)
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED THEN
+	DELETE
+;
+                QUERY PLAN                
+------------------------------------------
+ Merge on target t
+   ->  Hash Join
+         Hash Cond: (s.sid = t_1.tid)
+         ->  Seq Scan on source s
+         ->  Hash
+               ->  Seq Scan on target t_1
+(6 rows)
+
+EXPLAIN (COSTS OFF)
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT VALUES (4, NULL);
+                QUERY PLAN                
+------------------------------------------
+ Merge on target t
+   ->  Hash Left Join
+         Hash Cond: (s.sid = t_1.tid)
+         ->  Seq Scan on source s
+         ->  Hash
+               ->  Seq Scan on target t_1
+(6 rows)
+
+;
+DELETE FROM target WHERE tid > 100;
+ANALYZE target;
+-- insert some matching source rows to work from
+INSERT INTO source VALUES (2, 5);
+INSERT INTO source VALUES (3, 20);
+SELECT * FROM source ORDER BY sid;
+ sid | delta 
+-----+-------
+   2 |     5
+   3 |    20
+   4 |    40
+(3 rows)
+
+SELECT * FROM target ORDER BY tid;
+ tid | balance 
+-----+---------
+   1 |      10
+   2 |      20
+   3 |      30
+(3 rows)
+
+-- equivalent of an UPDATE join
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED THEN
+	UPDATE SET balance = 0
+;
+SELECT * FROM target ORDER BY tid;
+ tid | balance 
+-----+---------
+   1 |      10
+   2 |       0
+   3 |       0
+(3 rows)
+
+ROLLBACK;
+-- equivalent of a DELETE join
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED THEN
+	DELETE
+;
+SELECT * FROM target ORDER BY tid;
+ tid | balance 
+-----+---------
+   1 |      10
+(1 row)
+
+ROLLBACK;
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT VALUES (4, NULL)
+;
+SELECT * FROM target ORDER BY tid;
+ tid | balance 
+-----+---------
+   1 |      10
+   2 |      20
+   3 |      30
+   4 |        
+(4 rows)
+
+ROLLBACK;
+-- duplicate source row causes multiple target row update ERROR
+INSERT INTO source VALUES (2, 5);
+SELECT * FROM source ORDER BY sid;
+ sid | delta 
+-----+-------
+   2 |     5
+   2 |     5
+   3 |    20
+   4 |    40
+(4 rows)
+
+SELECT * FROM target ORDER BY tid;
+ tid | balance 
+-----+---------
+   1 |      10
+   2 |      20
+   3 |      30
+(3 rows)
+
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED THEN
+	UPDATE SET balance = 0
+;
+ERROR:  MERGE command cannot affect row a second time
+HINT:  Ensure that not more than one source row matches any one target row
+ROLLBACK;
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED THEN
+	DELETE
+;
+ERROR:  MERGE command cannot affect row a second time
+HINT:  Ensure that not more than one source row matches any one target row
+ROLLBACK;
+-- correct source data
+DELETE FROM source WHERE sid = 2;
+INSERT INTO source VALUES (2, 5);
+SELECT * FROM source ORDER BY sid;
+ sid | delta 
+-----+-------
+   2 |     5
+   3 |    20
+   4 |    40
+(3 rows)
+
+SELECT * FROM target ORDER BY tid;
+ tid | balance 
+-----+---------
+   1 |      10
+   2 |      20
+   3 |      30
+(3 rows)
+
+-- remove constraints
+alter table target drop CONSTRAINT target_pkey;
+alter table target alter column tid drop not null;
+-- multiple actions
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT VALUES (4, 4)
+WHEN MATCHED THEN
+	UPDATE SET balance = 0
+;
+SELECT * FROM target ORDER BY tid;
+ tid | balance 
+-----+---------
+   1 |      10
+   2 |       0
+   3 |       0
+   4 |       4
+(4 rows)
+
+ROLLBACK;
+-- should be equivalent
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED THEN
+	INSERT VALUES (4, 4);
+;
+SELECT * FROM target ORDER BY tid;
+ tid | balance 
+-----+---------
+   1 |      10
+   2 |       0
+   3 |       0
+   4 |       4
+(4 rows)
+
+ROLLBACK;
+-- column references
+-- do a simple equivalent of an UPDATE join
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED THEN
+	UPDATE SET balance = t.balance + s.delta
+;
+SELECT * FROM target ORDER BY tid;
+ tid | balance 
+-----+---------
+   1 |      10
+   2 |      25
+   3 |      50
+(3 rows)
+
+ROLLBACK;
+-- do a simple equivalent of an INSERT SELECT
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT VALUES (s.sid, s.delta)
+;
+SELECT * FROM target ORDER BY tid;
+ tid | balance 
+-----+---------
+   1 |      10
+   2 |      20
+   3 |      30
+   4 |      40
+(4 rows)
+
+ROLLBACK;
+-- and again with explicitly identified column list
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT (tid, balance) VALUES (s.sid, s.delta)
+;
+SELECT * FROM target ORDER BY tid;
+ tid | balance 
+-----+---------
+   1 |      10
+   2 |      20
+   3 |      30
+   4 |      40
+(4 rows)
+
+ROLLBACK;
+-- and again with a subtle error: referring to non-existent target row for NOT MATCHED
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT (tid, balance) VALUES (t.tid, s.delta)
+;
+ERROR:  invalid reference to FROM-clause entry for table "t"
+LINE 5:  INSERT (tid, balance) VALUES (t.tid, s.delta)
+                                       ^
+HINT:  There is an entry for table "t", but it cannot be referenced from this part of the query.
+-- and again with a constant ON clause
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON (SELECT true)
+WHEN NOT MATCHED THEN
+	INSERT (tid, balance) VALUES (t.tid, s.delta)
+;
+ERROR:  invalid reference to FROM-clause entry for table "t"
+LINE 5:  INSERT (tid, balance) VALUES (t.tid, s.delta)
+                                       ^
+HINT:  There is an entry for table "t", but it cannot be referenced from this part of the query.
+SELECT * FROM target ORDER BY tid;
+ERROR:  current transaction is aborted, commands ignored until end of transaction block
+ROLLBACK;
+-- now the classic UPSERT
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED THEN
+	UPDATE SET balance = t.balance + s.delta
+WHEN NOT MATCHED THEN
+	INSERT VALUES (s.sid, s.delta)
+;
+SELECT * FROM target ORDER BY tid;
+ tid | balance 
+-----+---------
+   1 |      10
+   2 |      25
+   3 |      50
+   4 |      40
+(4 rows)
+
+ROLLBACK;
+-- unreachable WHEN clause should ERROR
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED THEN /* Terminal WHEN clause for MATCHED */
+	DELETE
+WHEN MATCHED AND s.delta > 0 THEN
+	UPDATE SET balance = t.balance - s.delta
+;
+ERROR:  unreachable WHEN clause specified after unconditional WHEN clause
+ROLLBACK;
+-- conditional WHEN clause
+CREATE TABLE wq_target (tid integer not null, balance integer DEFAULT -1);
+CREATE TABLE wq_source (balance integer, sid integer);
+INSERT INTO wq_source (sid, balance) VALUES (1, 100);
+BEGIN;
+-- try a simple INSERT with default values first
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT (tid) VALUES (s.sid);
+SELECT * FROM wq_target;
+ tid | balance 
+-----+---------
+   1 |      -1
+(1 row)
+
+ROLLBACK;
+-- this time with a FALSE condition
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED AND FALSE THEN
+	INSERT (tid) VALUES (s.sid);
+SELECT * FROM wq_target;
+ tid | balance 
+-----+---------
+(0 rows)
+
+-- this time with an actual condition which returns false
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED AND s.balance <> 100 THEN
+	INSERT (tid) VALUES (s.sid);
+SELECT * FROM wq_target;
+ tid | balance 
+-----+---------
+(0 rows)
+
+BEGIN;
+-- and now with a condition which returns true
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED AND s.balance = 100 THEN
+	INSERT (tid) VALUES (s.sid);
+SELECT * FROM wq_target;
+ tid | balance 
+-----+---------
+   1 |      -1
+(1 row)
+
+ROLLBACK;
+-- conditions in the NOT MATCHED clause can only refer to source columns
+BEGIN;
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED AND t.balance = 100 THEN
+	INSERT (tid) VALUES (s.sid);
+ERROR:  invalid reference to FROM-clause entry for table "t"
+LINE 3: WHEN NOT MATCHED AND t.balance = 100 THEN
+                             ^
+HINT:  There is an entry for table "t", but it cannot be referenced from this part of the query.
+SELECT * FROM wq_target;
+ERROR:  current transaction is aborted, commands ignored until end of transaction block
+ROLLBACK;
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED AND s.balance = 100 THEN
+	INSERT (tid) VALUES (s.sid);
+SELECT * FROM wq_target;
+ tid | balance 
+-----+---------
+   1 |      -1
+(1 row)
+
+-- conditions in MATCHED clause can refer to both source and target
+SELECT * FROM wq_source;
+ balance | sid 
+---------+-----
+     100 |   1
+(1 row)
+
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN MATCHED AND s.balance = 100 THEN
+	UPDATE SET balance = t.balance + s.balance;
+SELECT * FROM wq_target;
+ tid | balance 
+-----+---------
+   1 |      99
+(1 row)
+
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN MATCHED AND t.balance = 100 THEN
+	UPDATE SET balance = t.balance + s.balance;
+SELECT * FROM wq_target;
+ tid | balance 
+-----+---------
+   1 |      99
+(1 row)
+
+-- check if AND works
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN MATCHED AND t.balance = 99 AND s.balance > 100 THEN
+	UPDATE SET balance = t.balance + s.balance;
+SELECT * FROM wq_target;
+ tid | balance 
+-----+---------
+   1 |      99
+(1 row)
+
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN MATCHED AND t.balance = 99 AND s.balance = 100 THEN
+	UPDATE SET balance = t.balance + s.balance;
+SELECT * FROM wq_target;
+ tid | balance 
+-----+---------
+   1 |     199
+(1 row)
+
+-- check if OR works
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN MATCHED AND t.balance = 99 OR s.balance > 100 THEN
+	UPDATE SET balance = t.balance + s.balance;
+SELECT * FROM wq_target;
+ tid | balance 
+-----+---------
+   1 |     199
+(1 row)
+
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN MATCHED AND t.balance = 199 OR s.balance > 100 THEN
+	UPDATE SET balance = t.balance + s.balance;
+SELECT * FROM wq_target;
+ tid | balance 
+-----+---------
+   1 |     299
+(1 row)
+
+-- check if subqueries work in the conditions?
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN MATCHED AND t.balance > (SELECT max(balance) FROM target) THEN
+	UPDATE SET balance = t.balance + s.balance;
+-- check if we can access system columns in the conditions
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN MATCHED AND t.xmin = t.xmax THEN
+	UPDATE SET balance = t.balance + s.balance;
+ERROR:  system column "xmin" reference in WHEN AND condition is invalid
+LINE 3: WHEN MATCHED AND t.xmin = t.xmax THEN
+                         ^
+-- test preventing WHEN AND conditions from writing to the database
+create or replace function merge_when_and_write() returns boolean
+language plpgsql as
+$$
+BEGIN
+	INSERT INTO target VALUES (100, 100);
+	RETURN TRUE;
+END;
+$$;
+BEGIN;
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN MATCHED AND (merge_when_and_write()) THEN
+	UPDATE SET balance = t.balance + s.balance;
+ROLLBACK;
+drop function merge_when_and_write();
+DROP TABLE wq_target, wq_source;
+-- test triggers
+create or replace function merge_trigfunc () returns trigger
+language plpgsql as
+$$
+BEGIN
+	RAISE NOTICE '% % % trigger', TG_WHEN, TG_OP, TG_LEVEL;
+	IF (TG_WHEN = 'BEFORE' AND TG_LEVEL = 'ROW') THEN
+		IF (TG_OP = 'DELETE') THEN
+			RETURN OLD;
+		ELSE
+			RETURN NEW;
+		END IF;
+	ELSE
+		RETURN NULL;
+	END IF;
+END;
+$$;
+CREATE TRIGGER merge_bsi BEFORE INSERT ON target FOR EACH STATEMENT EXECUTE PROCEDURE merge_trigfunc ();
+CREATE TRIGGER merge_bsu BEFORE UPDATE ON target FOR EACH STATEMENT EXECUTE PROCEDURE merge_trigfunc ();
+CREATE TRIGGER merge_bsd BEFORE DELETE ON target FOR EACH STATEMENT EXECUTE PROCEDURE merge_trigfunc ();
+CREATE TRIGGER merge_asi AFTER INSERT ON target FOR EACH STATEMENT EXECUTE PROCEDURE merge_trigfunc ();
+CREATE TRIGGER merge_asu AFTER UPDATE ON target FOR EACH STATEMENT EXECUTE PROCEDURE merge_trigfunc ();
+CREATE TRIGGER merge_asd AFTER DELETE ON target FOR EACH STATEMENT EXECUTE PROCEDURE merge_trigfunc ();
+CREATE TRIGGER merge_bri BEFORE INSERT ON target FOR EACH ROW EXECUTE PROCEDURE merge_trigfunc ();
+CREATE TRIGGER merge_bru BEFORE UPDATE ON target FOR EACH ROW EXECUTE PROCEDURE merge_trigfunc ();
+CREATE TRIGGER merge_brd BEFORE DELETE ON target FOR EACH ROW EXECUTE PROCEDURE merge_trigfunc ();
+CREATE TRIGGER merge_ari AFTER INSERT ON target FOR EACH ROW EXECUTE PROCEDURE merge_trigfunc ();
+CREATE TRIGGER merge_aru AFTER UPDATE ON target FOR EACH ROW EXECUTE PROCEDURE merge_trigfunc ();
+CREATE TRIGGER merge_ard AFTER DELETE ON target FOR EACH ROW EXECUTE PROCEDURE merge_trigfunc ();
+-- now the classic UPSERT, with a DELETE
+BEGIN;
+UPDATE target SET balance = 0 WHERE tid = 3;
+NOTICE:  BEFORE UPDATE STATEMENT trigger
+NOTICE:  BEFORE UPDATE ROW trigger
+NOTICE:  AFTER UPDATE ROW trigger
+NOTICE:  AFTER UPDATE STATEMENT trigger
+--EXPLAIN (ANALYZE ON, COSTS OFF, SUMMARY OFF, TIMING OFF)
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED AND t.balance > s.delta THEN
+	UPDATE SET balance = t.balance - s.delta
+WHEN MATCHED THEN
+	DELETE
+WHEN NOT MATCHED THEN
+	INSERT VALUES (s.sid, s.delta)
+;
+NOTICE:  BEFORE INSERT STATEMENT trigger
+NOTICE:  BEFORE UPDATE STATEMENT trigger
+NOTICE:  BEFORE DELETE STATEMENT trigger
+NOTICE:  BEFORE INSERT ROW trigger
+NOTICE:  BEFORE DELETE ROW trigger
+NOTICE:  BEFORE UPDATE ROW trigger
+NOTICE:  AFTER INSERT ROW trigger
+NOTICE:  AFTER DELETE ROW trigger
+NOTICE:  AFTER UPDATE ROW trigger
+NOTICE:  AFTER DELETE STATEMENT trigger
+NOTICE:  AFTER UPDATE STATEMENT trigger
+NOTICE:  AFTER INSERT STATEMENT trigger
+SELECT * FROM target ORDER BY tid;
+ tid | balance 
+-----+---------
+   1 |      10
+   2 |      15
+   4 |      40
+(3 rows)
+
+ROLLBACK;
+-- test from PL/pgSQL
+-- make sure MERGE INTO isn't interpreted to mean returning variables like SELECT INTO
+BEGIN;
+DO LANGUAGE plpgsql $$
+BEGIN
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED AND t.balance > s.delta THEN
+	UPDATE SET balance = t.balance - s.delta
+;
+END;
+$$;
+NOTICE:  BEFORE UPDATE STATEMENT trigger
+NOTICE:  BEFORE UPDATE ROW trigger
+NOTICE:  BEFORE UPDATE ROW trigger
+NOTICE:  AFTER UPDATE ROW trigger
+NOTICE:  AFTER UPDATE ROW trigger
+NOTICE:  AFTER UPDATE STATEMENT trigger
+ROLLBACK;
+--source constants
+BEGIN;
+MERGE INTO target t
+USING (SELECT 9 AS sid, 57 AS delta) AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT (tid, balance) VALUES (s.sid, s.delta)
+;
+NOTICE:  BEFORE INSERT STATEMENT trigger
+NOTICE:  BEFORE INSERT ROW trigger
+NOTICE:  AFTER INSERT ROW trigger
+NOTICE:  AFTER INSERT STATEMENT trigger
+SELECT * FROM target ORDER BY tid;
+ tid | balance 
+-----+---------
+   1 |      10
+   2 |      20
+   3 |      30
+   9 |      57
+(4 rows)
+
+ROLLBACK;
+--source query
+BEGIN;
+MERGE INTO target t
+USING (SELECT sid, delta FROM source WHERE delta > 0) AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT (tid, balance) VALUES (s.sid, s.delta)
+;
+NOTICE:  BEFORE INSERT STATEMENT trigger
+NOTICE:  BEFORE INSERT ROW trigger
+NOTICE:  AFTER INSERT ROW trigger
+NOTICE:  AFTER INSERT STATEMENT trigger
+SELECT * FROM target ORDER BY tid;
+ tid | balance 
+-----+---------
+   1 |      10
+   2 |      20
+   3 |      30
+   4 |      40
+(4 rows)
+
+ROLLBACK;
+BEGIN;
+MERGE INTO target t
+USING (SELECT sid, delta as newname FROM source WHERE delta > 0) AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT (tid, balance) VALUES (s.sid, s.newname)
+;
+NOTICE:  BEFORE INSERT STATEMENT trigger
+NOTICE:  BEFORE INSERT ROW trigger
+NOTICE:  AFTER INSERT ROW trigger
+NOTICE:  AFTER INSERT STATEMENT trigger
+SELECT * FROM target ORDER BY tid;
+ tid | balance 
+-----+---------
+   1 |      10
+   2 |      20
+   3 |      30
+   4 |      40
+(4 rows)
+
+ROLLBACK;
+--self-merge
+BEGIN;
+MERGE INTO target t1
+USING target t2
+ON t1.tid = t2.tid
+WHEN MATCHED THEN
+	UPDATE SET balance = t1.balance + t2.balance
+WHEN NOT MATCHED THEN
+	INSERT VALUES (t2.tid, t2.balance)
+;
+NOTICE:  BEFORE INSERT STATEMENT trigger
+NOTICE:  BEFORE UPDATE STATEMENT trigger
+NOTICE:  BEFORE UPDATE ROW trigger
+NOTICE:  BEFORE UPDATE ROW trigger
+NOTICE:  BEFORE UPDATE ROW trigger
+NOTICE:  AFTER UPDATE ROW trigger
+NOTICE:  AFTER UPDATE ROW trigger
+NOTICE:  AFTER UPDATE ROW trigger
+NOTICE:  AFTER UPDATE STATEMENT trigger
+NOTICE:  AFTER INSERT STATEMENT trigger
+SELECT * FROM target ORDER BY tid;
+ tid | balance 
+-----+---------
+   1 |      20
+   2 |      40
+   3 |      60
+(3 rows)
+
+ROLLBACK;
+BEGIN;
+MERGE INTO target t
+USING (SELECT tid as sid, balance as delta FROM target WHERE balance > 0) AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT (tid, balance) VALUES (s.sid, s.delta)
+;
+NOTICE:  BEFORE INSERT STATEMENT trigger
+NOTICE:  AFTER INSERT STATEMENT trigger
+SELECT * FROM target ORDER BY tid;
+ tid | balance 
+-----+---------
+   1 |      10
+   2 |      20
+   3 |      30
+(3 rows)
+
+ROLLBACK;
+BEGIN;
+MERGE INTO target t
+USING
+(SELECT sid, max(delta) AS delta
+ FROM source
+ GROUP BY sid
+ HAVING count(*) = 1
+ ORDER BY sid ASC) AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT (tid, balance) VALUES (s.sid, s.delta)
+;
+NOTICE:  BEFORE INSERT STATEMENT trigger
+NOTICE:  BEFORE INSERT ROW trigger
+NOTICE:  AFTER INSERT ROW trigger
+NOTICE:  AFTER INSERT STATEMENT trigger
+SELECT * FROM target ORDER BY tid;
+ tid | balance 
+-----+---------
+   1 |      10
+   2 |      20
+   3 |      30
+   4 |      40
+(4 rows)
+
+ROLLBACK;
+-- plpgsql parameters and results
+BEGIN;
+CREATE FUNCTION merge_func (p_id integer, p_bal integer)
+RETURNS INTEGER
+LANGUAGE plpgsql
+AS $$
+DECLARE
+ result integer;
+BEGIN
+MERGE INTO target t
+USING (SELECT p_id AS sid) AS s
+ON t.tid = s.sid
+WHEN MATCHED THEN
+	UPDATE SET balance = t.balance - p_bal
+;
+IF FOUND THEN
+	GET DIAGNOSTICS result := ROW_COUNT;
+END IF;
+RETURN result;
+END;
+$$;
+SELECT merge_func(3, 4);
+NOTICE:  BEFORE UPDATE STATEMENT trigger
+NOTICE:  BEFORE UPDATE ROW trigger
+NOTICE:  AFTER UPDATE ROW trigger
+NOTICE:  AFTER UPDATE STATEMENT trigger
+ merge_func 
+------------
+          1
+(1 row)
+
+SELECT * FROM target ORDER BY tid;
+ tid | balance 
+-----+---------
+   1 |      10
+   2 |      20
+   3 |      26
+(3 rows)
+
+ROLLBACK;
+-- PREPARE
+BEGIN;
+prepare foom as merge into target t using (select 1 as sid) s on (t.tid = s.sid) when matched then update set balance = 1;
+execute foom;
+NOTICE:  BEFORE UPDATE STATEMENT trigger
+NOTICE:  BEFORE UPDATE ROW trigger
+NOTICE:  AFTER UPDATE ROW trigger
+NOTICE:  AFTER UPDATE STATEMENT trigger
+SELECT * FROM target ORDER BY tid;
+ tid | balance 
+-----+---------
+   1 |       1
+   2 |      20
+   3 |      30
+(3 rows)
+
+ROLLBACK;
+BEGIN;
+PREPARE foom2 (integer, integer) AS
+MERGE INTO target t
+USING (SELECT 1) s
+ON t.tid = $1
+WHEN MATCHED THEN
+UPDATE SET balance = $2;
+--EXPLAIN (ANALYZE ON, COSTS OFF, SUMMARY OFF, TIMING OFF)
+execute foom2 (1, 1);
+NOTICE:  BEFORE UPDATE STATEMENT trigger
+NOTICE:  BEFORE UPDATE ROW trigger
+NOTICE:  AFTER UPDATE ROW trigger
+NOTICE:  AFTER UPDATE STATEMENT trigger
+SELECT * FROM target ORDER BY tid;
+ tid | balance 
+-----+---------
+   1 |       1
+   2 |      20
+   3 |      30
+(3 rows)
+
+ROLLBACK;
+-- subqueries in source relation
+CREATE TABLE sq_target (tid integer NOT NULL, balance integer);
+CREATE TABLE sq_source (delta integer, sid integer, balance integer DEFAULT 0);
+INSERT INTO sq_target(tid, balance) VALUES (1,100), (2,200), (3,300);
+INSERT INTO sq_source(sid, delta) VALUES (1,10), (2,20), (4,40);
+BEGIN;
+MERGE INTO sq_target t
+USING (SELECT * FROM sq_source) s
+ON tid = sid
+WHEN MATCHED AND t.balance > delta THEN
+	UPDATE SET balance = t.balance + delta;
+SELECT * FROM sq_target;
+ tid | balance 
+-----+---------
+   3 |     300
+   1 |     110
+   2 |     220
+(3 rows)
+
+ROLLBACK;
+-- try a view
+CREATE VIEW v AS SELECT * FROM sq_source WHERE sid < 2;
+BEGIN;
+MERGE INTO sq_target
+USING v
+ON tid = sid
+WHEN MATCHED THEN
+    UPDATE SET balance = v.balance + delta;
+SELECT * FROM sq_target;
+ tid | balance 
+-----+---------
+   2 |     200
+   3 |     300
+   1 |      10
+(3 rows)
+
+ROLLBACK;
+-- ambiguous reference to a column
+BEGIN;
+MERGE INTO sq_target
+USING v
+ON tid = sid
+WHEN MATCHED AND tid > 2 THEN
+    UPDATE SET balance = balance + delta
+WHEN NOT MATCHED THEN
+	INSERT (balance, tid) VALUES (balance + delta, sid)
+WHEN MATCHED AND tid < 2 THEN
+	DELETE;
+ERROR:  column reference "balance" is ambiguous
+LINE 5:     UPDATE SET balance = balance + delta
+                                 ^
+ROLLBACK;
+BEGIN;
+INSERT INTO sq_source (sid, balance, delta) VALUES (-1, -1, -10);
+MERGE INTO sq_target t
+USING v
+ON tid = sid
+WHEN MATCHED AND tid > 2 THEN
+    UPDATE SET balance = t.balance + delta
+WHEN NOT MATCHED THEN
+	INSERT (balance, tid) VALUES (balance + delta, sid)
+WHEN MATCHED AND tid < 2 THEN
+	DELETE;
+SELECT * FROM sq_target;
+ tid | balance 
+-----+---------
+   2 |     200
+   3 |     300
+  -1 |     -11
+(3 rows)
+
+ROLLBACK;
+-- CTEs
+BEGIN;
+INSERT INTO sq_source (sid, balance, delta) VALUES (-1, -1, -10);
+WITH targq AS (
+	SELECT * FROM v
+)
+MERGE INTO sq_target t
+USING v
+ON tid = sid
+WHEN MATCHED AND tid > 2 THEN
+    UPDATE SET balance = t.balance + delta
+WHEN NOT MATCHED THEN
+	INSERT (balance, tid) VALUES (balance + delta, sid)
+WHEN MATCHED AND tid < 2 THEN
+	DELETE
+;
+ROLLBACK;
+-- RETURNING
+BEGIN;
+INSERT INTO sq_source (sid, balance, delta) VALUES (-1, -1, -10);
+MERGE INTO sq_target t
+USING v
+ON tid = sid
+WHEN MATCHED AND tid > 2 THEN
+    UPDATE SET balance = t.balance + delta
+WHEN NOT MATCHED THEN
+	INSERT (balance, tid) VALUES (balance + delta, sid)
+WHEN MATCHED AND tid < 2 THEN
+	DELETE
+RETURNING *
+;
+ERROR:  syntax error at or near "RETURNING"
+LINE 10: RETURNING *
+         ^
+ROLLBACK;
+-- EXPLAIN
+CREATE TABLE ex_mtarget (a int, b int);
+CREATE TABLE ex_msource (a int, b int);
+INSERT INTO ex_mtarget SELECT i, i*10 FROM generate_series(1,100,2) i;
+INSERT INTO ex_msource SELECT i, i*10 FROM generate_series(1,100,1) i;
+-- only updates
+--EXPLAIN (ANALYZE ON, COSTS OFF, SUMMARY OFF, TIMING OFF)
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN MATCHED THEN
+	UPDATE SET b = t.b + 1;
+-- only updates to selected tuples
+--EXPLAIN (ANALYZE ON, COSTS OFF, SUMMARY OFF, TIMING OFF)
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN MATCHED AND t.a < 10 THEN
+	UPDATE SET b = t.b + 1;
+-- updates + deletes
+--EXPLAIN (ANALYZE ON, COSTS OFF, SUMMARY OFF, TIMING OFF)
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN MATCHED AND t.a < 10 THEN
+	UPDATE SET b = t.b + 1
+WHEN MATCHED AND t.a >= 10 AND t.a <= 20 THEN
+	DELETE;
+-- only inserts
+--EXPLAIN (ANALYZE ON, COSTS OFF, SUMMARY OFF, TIMING OFF)
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED AND s.a < 10 THEN
+	INSERT VALUES (a, b);
+-- all three
+--EXPLAIN (ANALYZE ON, COSTS OFF, SUMMARY OFF, TIMING OFF)
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN MATCHED AND t.a < 10 THEN
+	UPDATE SET b = t.b + 1
+WHEN MATCHED AND t.a >= 30 AND t.a <= 40 THEN
+	DELETE
+WHEN NOT MATCHED AND s.a < 20 THEN
+	INSERT VALUES (a, b);
+DROP TABLE ex_msource, ex_mtarget;
+-- Subqueries
+BEGIN;
+MERGE INTO sq_target t
+USING v
+ON tid = sid
+WHEN MATCHED THEN
+    UPDATE SET balance = (SELECT count(*) FROM sq_target)
+;
+SELECT * FROM sq_target WHERE tid = 1;
+ tid | balance 
+-----+---------
+   1 |       3
+(1 row)
+
+ROLLBACK;
+BEGIN;
+MERGE INTO sq_target t
+USING v
+ON tid = sid
+WHEN MATCHED AND (SELECT count(*) > 0 FROM sq_target) THEN
+    UPDATE SET balance = 42
+;
+SELECT * FROM sq_target WHERE tid = 1;
+ tid | balance 
+-----+---------
+   1 |      42
+(1 row)
+
+ROLLBACK;
+BEGIN;
+MERGE INTO sq_target t
+USING v
+ON tid = sid AND (SELECT count(*) > 0 FROM sq_target)
+WHEN MATCHED THEN
+    UPDATE SET balance = 42
+;
+SELECT * FROM sq_target WHERE tid = 1;
+ tid | balance 
+-----+---------
+   1 |      42
+(1 row)
+
+ROLLBACK;
+DROP TABLE sq_target, sq_source CASCADE;
+NOTICE:  drop cascades to view v
+CREATE TABLE pa_target (tid integer, balance float, val text)
+	PARTITION BY LIST (tid);
+CREATE TABLE part1 PARTITION OF pa_target FOR VALUES IN (1,4);
+CREATE TABLE part2 PARTITION OF pa_target FOR VALUES IN (2,5,6);
+CREATE TABLE part3 PARTITION OF pa_target FOR VALUES IN (3,8,9);
+CREATE TABLE part4 PARTITION OF pa_target DEFAULT;
+CREATE TABLE pa_source (sid integer, delta float);
+-- insert many rows to the source table
+INSERT INTO pa_source SELECT id, id * 10  FROM generate_series(1,14) AS id;
+-- insert a few rows in the target table (odd numbered tid)
+INSERT INTO pa_target SELECT id, id * 100, 'initial' FROM generate_series(1,14,2) AS id;
+-- try simple MERGE
+BEGIN;
+MERGE INTO pa_target t
+  USING pa_source s
+  ON t.tid = s.sid
+  WHEN MATCHED THEN
+    UPDATE SET balance = balance + delta, val = val || ' updated by merge'
+  WHEN NOT MATCHED THEN
+    INSERT VALUES (sid, delta, 'inserted by merge');
+SELECT * FROM pa_target ORDER BY tid;
+ tid | balance |           val            
+-----+---------+--------------------------
+   1 |     110 | initial updated by merge
+   2 |      20 | inserted by merge
+   3 |     330 | initial updated by merge
+   4 |      40 | inserted by merge
+   5 |     550 | initial updated by merge
+   6 |      60 | inserted by merge
+   7 |     770 | initial updated by merge
+   8 |      80 | inserted by merge
+   9 |     990 | initial updated by merge
+  10 |     100 | inserted by merge
+  11 |    1210 | initial updated by merge
+  12 |     120 | inserted by merge
+  13 |    1430 | initial updated by merge
+  14 |     140 | inserted by merge
+(14 rows)
+
+ROLLBACK;
+-- same with a constant qual
+BEGIN;
+MERGE INTO pa_target t
+  USING pa_source s
+  ON t.tid = s.sid AND tid = 1
+  WHEN MATCHED THEN
+    UPDATE SET balance = balance + delta, val = val || ' updated by merge'
+  WHEN NOT MATCHED THEN
+    INSERT VALUES (sid, delta, 'inserted by merge');
+SELECT * FROM pa_target ORDER BY tid;
+ tid | balance |           val            
+-----+---------+--------------------------
+   1 |     110 | initial updated by merge
+   2 |      20 | inserted by merge
+   3 |      30 | inserted by merge
+   3 |     300 | initial
+   4 |      40 | inserted by merge
+   5 |     500 | initial
+   5 |      50 | inserted by merge
+   6 |      60 | inserted by merge
+   7 |     700 | initial
+   7 |      70 | inserted by merge
+   8 |      80 | inserted by merge
+   9 |      90 | inserted by merge
+   9 |     900 | initial
+  10 |     100 | inserted by merge
+  11 |    1100 | initial
+  11 |     110 | inserted by merge
+  12 |     120 | inserted by merge
+  13 |    1300 | initial
+  13 |     130 | inserted by merge
+  14 |     140 | inserted by merge
+(20 rows)
+
+ROLLBACK;
+-- try updating the partition key column
+BEGIN;
+MERGE INTO pa_target t
+  USING pa_source s
+  ON t.tid = s.sid
+  WHEN MATCHED THEN
+    UPDATE SET tid = tid + 1, balance = balance + delta, val = val || ' updated by merge'
+  WHEN NOT MATCHED THEN
+    INSERT VALUES (sid, delta, 'inserted by merge');
+SELECT * FROM pa_target ORDER BY tid;
+ tid | balance |           val            
+-----+---------+--------------------------
+   2 |     110 | initial updated by merge
+   2 |      20 | inserted by merge
+   4 |      40 | inserted by merge
+   4 |     330 | initial updated by merge
+   6 |     550 | initial updated by merge
+   6 |      60 | inserted by merge
+   8 |      80 | inserted by merge
+   8 |     770 | initial updated by merge
+  10 |     990 | initial updated by merge
+  10 |     100 | inserted by merge
+  12 |    1210 | initial updated by merge
+  12 |     120 | inserted by merge
+  14 |    1430 | initial updated by merge
+  14 |     140 | inserted by merge
+(14 rows)
+
+ROLLBACK;
+DROP TABLE pa_target CASCADE;
+-- The target table is partitioned in the same way, but this time by attaching
+-- partitions which have columns in different order, dropped columns etc.
+CREATE TABLE pa_target (tid integer, balance float, val text)
+	PARTITION BY LIST (tid);
+CREATE TABLE part1 (tid integer, balance float, val text);
+CREATE TABLE part2 (balance float, tid integer, val text);
+CREATE TABLE part3 (tid integer, balance float, val text);
+CREATE TABLE part4 (extraid text, tid integer, balance float, val text);
+ALTER TABLE part4 DROP COLUMN extraid;
+ALTER TABLE pa_target ATTACH PARTITION part1 FOR VALUES IN (1,4);
+ALTER TABLE pa_target ATTACH PARTITION part2 FOR VALUES IN (2,5,6);
+ALTER TABLE pa_target ATTACH PARTITION part3 FOR VALUES IN (3,8,9);
+ALTER TABLE pa_target ATTACH PARTITION part4 DEFAULT;
+-- insert a few rows in the target table (odd numbered tid)
+INSERT INTO pa_target SELECT id, id * 100, 'initial' FROM generate_series(1,14,2) AS id;
+-- try simple MERGE
+BEGIN;
+MERGE INTO pa_target t
+  USING pa_source s
+  ON t.tid = s.sid
+  WHEN MATCHED THEN
+    UPDATE SET balance = balance + delta, val = val || ' updated by merge'
+  WHEN NOT MATCHED THEN
+    INSERT VALUES (sid, delta, 'inserted by merge');
+SELECT * FROM pa_target ORDER BY tid;
+ tid | balance |           val            
+-----+---------+--------------------------
+   1 |     110 | initial updated by merge
+   2 |      20 | inserted by merge
+   3 |     330 | initial updated by merge
+   4 |      40 | inserted by merge
+   5 |     550 | initial updated by merge
+   6 |      60 | inserted by merge
+   7 |     770 | initial updated by merge
+   8 |      80 | inserted by merge
+   9 |     990 | initial updated by merge
+  10 |     100 | inserted by merge
+  11 |    1210 | initial updated by merge
+  12 |     120 | inserted by merge
+  13 |    1430 | initial updated by merge
+  14 |     140 | inserted by merge
+(14 rows)
+
+ROLLBACK;
+-- same with a constant qual
+BEGIN;
+MERGE INTO pa_target t
+  USING pa_source s
+  ON t.tid = s.sid AND tid = 1
+  WHEN MATCHED THEN
+    UPDATE SET balance = balance + delta, val = val || ' updated by merge'
+  WHEN NOT MATCHED THEN
+    INSERT VALUES (sid, delta, 'inserted by merge');
+SELECT * FROM pa_target ORDER BY tid;
+ tid | balance |           val            
+-----+---------+--------------------------
+   1 |     110 | initial updated by merge
+   2 |      20 | inserted by merge
+   3 |      30 | inserted by merge
+   3 |     300 | initial
+   4 |      40 | inserted by merge
+   5 |     500 | initial
+   5 |      50 | inserted by merge
+   6 |      60 | inserted by merge
+   7 |     700 | initial
+   7 |      70 | inserted by merge
+   8 |      80 | inserted by merge
+   9 |      90 | inserted by merge
+   9 |     900 | initial
+  10 |     100 | inserted by merge
+  11 |    1100 | initial
+  11 |     110 | inserted by merge
+  12 |     120 | inserted by merge
+  13 |    1300 | initial
+  13 |     130 | inserted by merge
+  14 |     140 | inserted by merge
+(20 rows)
+
+ROLLBACK;
+-- try updating the partition key column
+BEGIN;
+MERGE INTO pa_target t
+  USING pa_source s
+  ON t.tid = s.sid
+  WHEN MATCHED THEN
+    UPDATE SET tid = tid + 1, balance = balance + delta, val = val || ' updated by merge'
+  WHEN NOT MATCHED THEN
+    INSERT VALUES (sid, delta, 'inserted by merge');
+SELECT * FROM pa_target ORDER BY tid;
+ tid | balance |           val            
+-----+---------+--------------------------
+   2 |     110 | initial updated by merge
+   2 |      20 | inserted by merge
+   4 |      40 | inserted by merge
+   4 |     330 | initial updated by merge
+   6 |     550 | initial updated by merge
+   6 |      60 | inserted by merge
+   8 |      80 | inserted by merge
+   8 |     770 | initial updated by merge
+  10 |     990 | initial updated by merge
+  10 |     100 | inserted by merge
+  12 |    1210 | initial updated by merge
+  12 |     120 | inserted by merge
+  14 |    1430 | initial updated by merge
+  14 |     140 | inserted by merge
+(14 rows)
+
+ROLLBACK;
+DROP TABLE pa_source;
+DROP TABLE pa_target CASCADE;
+-- Sub-partitionin
+CREATE TABLE pa_target (logts timestamp, tid integer, balance float, val text)
+	PARTITION BY RANGE (logts);
+CREATE TABLE part_m01 PARTITION OF pa_target
+	FOR VALUES FROM ('2017-01-01') TO ('2017-02-01')
+	PARTITION BY LIST (tid);
+CREATE TABLE part_m01_odd PARTITION OF part_m01
+	FOR VALUES IN (1,3,5,7,9);
+CREATE TABLE part_m01_even PARTITION OF part_m01
+	FOR VALUES IN (2,4,6,8);
+CREATE TABLE part_m02 PARTITION OF pa_target
+	FOR VALUES FROM ('2017-02-01') TO ('2017-03-01')
+	PARTITION BY LIST (tid);
+CREATE TABLE part_m02_odd PARTITION OF part_m02
+	FOR VALUES IN (1,3,5,7,9);
+CREATE TABLE part_m02_even PARTITION OF part_m02
+	FOR VALUES IN (2,4,6,8);
+CREATE TABLE pa_source (sid integer, delta float);
+-- insert many rows to the source table
+INSERT INTO pa_source SELECT id, id * 10  FROM generate_series(1,14) AS id;
+-- insert a few rows in the target table (odd numbered tid)
+INSERT INTO pa_target SELECT '2017-01-31', id, id * 100, 'initial' FROM generate_series(1,9,3) AS id;
+INSERT INTO pa_target SELECT '2017-02-28', id, id * 100, 'initial' FROM generate_series(2,9,3) AS id;
+-- try simple MERGE
+BEGIN;
+MERGE INTO pa_target t
+  USING (SELECT '2017-01-15' AS slogts, * FROM pa_source WHERE sid < 10) s
+  ON t.tid = s.sid
+  WHEN MATCHED THEN
+    UPDATE SET balance = balance + delta, val = val || ' updated by merge'
+  WHEN NOT MATCHED THEN
+    INSERT VALUES (slogts::timestamp, sid, delta, 'inserted by merge');
+SELECT * FROM pa_target ORDER BY tid;
+          logts           | tid | balance |           val            
+--------------------------+-----+---------+--------------------------
+ Tue Jan 31 00:00:00 2017 |   1 |     110 | initial updated by merge
+ Tue Feb 28 00:00:00 2017 |   2 |     220 | initial updated by merge
+ Sun Jan 15 00:00:00 2017 |   3 |      30 | inserted by merge
+ Tue Jan 31 00:00:00 2017 |   4 |     440 | initial updated by merge
+ Tue Feb 28 00:00:00 2017 |   5 |     550 | initial updated by merge
+ Sun Jan 15 00:00:00 2017 |   6 |      60 | inserted by merge
+ Tue Jan 31 00:00:00 2017 |   7 |     770 | initial updated by merge
+ Tue Feb 28 00:00:00 2017 |   8 |     880 | initial updated by merge
+ Sun Jan 15 00:00:00 2017 |   9 |      90 | inserted by merge
+(9 rows)
+
+ROLLBACK;
+DROP TABLE pa_source;
+DROP TABLE pa_target CASCADE;
+-- some complex joins on the source side
+CREATE TABLE cj_target (tid integer, balance float, val text);
+CREATE TABLE cj_source1 (sid1 integer, scat integer, delta integer);
+CREATE TABLE cj_source2 (sid2 integer, sval text);
+INSERT INTO cj_source1 VALUES (1, 10, 100);
+INSERT INTO cj_source1 VALUES (1, 20, 200);
+INSERT INTO cj_source1 VALUES (2, 20, 300);
+INSERT INTO cj_source1 VALUES (3, 10, 400);
+INSERT INTO cj_source2 VALUES (1, 'initial source2');
+INSERT INTO cj_source2 VALUES (2, 'initial source2');
+INSERT INTO cj_source2 VALUES (3, 'initial source2');
+-- source relation is an unalised join
+MERGE INTO cj_target t
+USING cj_source1 s1
+	INNER JOIN cj_source2 s2 ON sid1 = sid2
+ON t.tid = sid1
+WHEN NOT MATCHED THEN
+	INSERT VALUES (sid1, delta, sval);
+-- try accessing columns from either side of the source join
+MERGE INTO cj_target t
+USING cj_source2 s2
+	INNER JOIN cj_source1 s1 ON sid1 = sid2 AND scat = 20
+ON t.tid = sid1
+WHEN NOT MATCHED THEN
+	INSERT VALUES (sid2, delta, sval)
+WHEN MATCHED THEN
+	DELETE;
+-- some simple expressions in INSERT targetlist
+MERGE INTO cj_target t
+USING cj_source2 s2
+	INNER JOIN cj_source1 s1 ON sid1 = sid2
+ON t.tid = sid1
+WHEN NOT MATCHED THEN
+	INSERT VALUES (sid2, delta + scat, sval)
+WHEN MATCHED THEN
+	UPDATE SET val = val || ' updated by merge';
+MERGE INTO cj_target t
+USING cj_source2 s2
+	INNER JOIN cj_source1 s1 ON sid1 = sid2 AND scat = 20
+ON t.tid = sid1
+WHEN MATCHED THEN
+	UPDATE SET val = val || ' ' || delta::text;
+SELECT * FROM cj_target;
+ tid | balance |               val                
+-----+---------+----------------------------------
+   3 |     400 | initial source2 updated by merge
+   1 |     220 | initial source2 200
+   1 |     110 | initial source2 200
+   2 |     320 | initial source2 300
+(4 rows)
+
+ALTER TABLE cj_source1 RENAME COLUMN sid1 TO sid;
+ALTER TABLE cj_source2 RENAME COLUMN sid2 TO sid;
+TRUNCATE cj_target;
+MERGE INTO cj_target t
+USING cj_source1 s1
+	INNER JOIN cj_source2 s2 ON s1.sid = s2.sid
+ON t.tid = s1.sid
+WHEN NOT MATCHED THEN
+	INSERT VALUES (s2.sid, delta, sval);
+DROP TABLE cj_source2, cj_source1, cj_target;
+-- Function scans
+CREATE TABLE fs_target (a int, b int, c text);
+MERGE INTO fs_target t
+USING generate_series(1,100,1) AS id
+ON t.a = id
+WHEN MATCHED THEN
+	UPDATE SET b = b + id
+WHEN NOT MATCHED THEN
+	INSERT VALUES (id, -1);
+MERGE INTO fs_target t
+USING generate_series(1,100,2) AS id
+ON t.a = id
+WHEN MATCHED THEN
+	UPDATE SET b = b + id, c = 'updated '|| id.*::text
+WHEN NOT MATCHED THEN
+	INSERT VALUES (id, -1, 'inserted ' || id.*::text);
+SELECT count(*) FROM fs_target;
+ count 
+-------
+   100
+(1 row)
+
+DROP TABLE fs_target;
+-- SERIALIZABLE test
+-- handled in isolation tests
+-- prepare
+RESET SESSION AUTHORIZATION;
+DROP TABLE target, target2;
+DROP TABLE source, source2;
+DROP FUNCTION merge_trigfunc();
+DROP USER merge_privs;
+DROP USER merge_no_privs;
diff --git a/src/test/regress/expected/privileges.out b/src/test/regress/expected/privileges.out
index 83b3196b1d..1f284c0bba 100644
--- a/src/test/regress/expected/privileges.out
+++ b/src/test/regress/expected/privileges.out
@@ -517,6 +517,104 @@ SELECT atest6 FROM atest6; -- ok
 (0 rows)
 
 COPY atest6 TO stdout; -- ok
+-- test column privileges with MERGE
+SET SESSION AUTHORIZATION regress_priv_user1;
+CREATE TABLE mtarget (a int, b text);
+CREATE TABLE msource (a int, b text);
+INSERT INTO mtarget VALUES (1, 'init1'), (2, 'init2');
+INSERT INTO msource VALUES (1, 'source1'), (2, 'source2'), (3, 'source3');
+GRANT SELECT (a) ON msource TO regress_priv_user4;
+GRANT SELECT (a) ON mtarget TO regress_priv_user4;
+GRANT INSERT (a,b) ON mtarget TO regress_priv_user4;
+GRANT UPDATE (b) ON mtarget TO regress_priv_user4;
+SET SESSION AUTHORIZATION regress_priv_user4;
+--
+-- test source privileges
+--
+-- fail (no SELECT priv on s.b)
+MERGE INTO mtarget t USING msource s ON t.a = s.a
+WHEN MATCHED THEN
+	UPDATE SET b = s.b
+WHEN NOT MATCHED THEN
+	INSERT VALUES (a, NULL);
+ERROR:  permission denied for table msource
+-- fail (s.b used in the INSERTed values)
+MERGE INTO mtarget t USING msource s ON t.a = s.a
+WHEN MATCHED THEN
+	UPDATE SET b = 'x'
+WHEN NOT MATCHED THEN
+	INSERT VALUES (a, b);
+ERROR:  permission denied for table msource
+-- fail (s.b used in the WHEN quals)
+MERGE INTO mtarget t USING msource s ON t.a = s.a
+WHEN MATCHED AND s.b = 'x' THEN
+	UPDATE SET b = 'x'
+WHEN NOT MATCHED THEN
+	INSERT VALUES (a, NULL);
+ERROR:  permission denied for table msource
+-- this should be ok since only s.a is accessed
+BEGIN;
+MERGE INTO mtarget t USING msource s ON t.a = s.a
+WHEN MATCHED THEN
+	UPDATE SET b = 'ok'
+WHEN NOT MATCHED THEN
+	INSERT VALUES (a, NULL);
+ROLLBACK;
+SET SESSION AUTHORIZATION regress_priv_user1;
+GRANT SELECT (b) ON msource TO regress_priv_user4;
+SET SESSION AUTHORIZATION regress_priv_user4;
+-- should now be ok
+BEGIN;
+MERGE INTO mtarget t USING msource s ON t.a = s.a
+WHEN MATCHED THEN
+	UPDATE SET b = s.b
+WHEN NOT MATCHED THEN
+	INSERT VALUES (a, b);
+ROLLBACK;
+--
+-- test target privileges
+--
+-- fail (no SELECT priv on t.b)
+MERGE INTO mtarget t USING msource s ON t.a = s.a
+WHEN MATCHED THEN
+	UPDATE SET b = t.b
+WHEN NOT MATCHED THEN
+	INSERT VALUES (a, NULL);
+ERROR:  permission denied for table mtarget
+-- fail (no UPDATE on t.a)
+MERGE INTO mtarget t USING msource s ON t.a = s.a
+WHEN MATCHED THEN
+	UPDATE SET b = s.b, a = t.a + 1
+WHEN NOT MATCHED THEN
+	INSERT VALUES (a, b);
+ERROR:  permission denied for table mtarget
+-- fail (no SELECT on t.b)
+MERGE INTO mtarget t USING msource s ON t.a = s.a
+WHEN MATCHED AND t.b IS NOT NULL THEN
+	UPDATE SET b = s.b
+WHEN NOT MATCHED THEN
+	INSERT VALUES (a, b);
+ERROR:  permission denied for table mtarget
+-- ok
+BEGIN;
+MERGE INTO mtarget t USING msource s ON t.a = s.a
+WHEN MATCHED THEN
+	UPDATE SET b = s.b;
+ROLLBACK;
+-- fail (no DELETE)
+MERGE INTO mtarget t USING msource s ON t.a = s.a
+WHEN MATCHED AND t.b IS NOT NULL THEN
+	DELETE;
+ERROR:  permission denied for table mtarget
+-- grant delete privileges
+SET SESSION AUTHORIZATION regress_priv_user1;
+GRANT DELETE ON mtarget TO regress_priv_user4;
+-- should be ok now
+BEGIN;
+MERGE INTO mtarget t USING msource s ON t.a = s.a
+WHEN MATCHED AND t.b IS NOT NULL THEN
+	DELETE;
+ROLLBACK;
 -- check error reporting with column privs
 SET SESSION AUTHORIZATION regress_priv_user1;
 CREATE TABLE t1 (c1 int, c2 int, c3 int check (c3 < 5), primary key (c1, c2));
diff --git a/src/test/regress/expected/rowsecurity.out b/src/test/regress/expected/rowsecurity.out
index 1d12b01068..76d4d16c9e 100644
--- a/src/test/regress/expected/rowsecurity.out
+++ b/src/test/regress/expected/rowsecurity.out
@@ -2138,6 +2138,188 @@ ERROR:  new row violates row-level security policy (USING expression) for table
 INSERT INTO document VALUES (1, (SELECT cid from category WHERE cname = 'novel'), 1, 'regress_rls_bob', 'my first novel')
     ON CONFLICT (did) DO UPDATE SET dauthor = 'regress_rls_carol';
 ERROR:  new row violates row-level security policy for table "document"
+--
+-- MERGE
+--
+RESET SESSION AUTHORIZATION;
+DROP POLICY p3_with_all ON document;
+ALTER TABLE document ADD COLUMN dnotes text DEFAULT '';
+-- all documents are readable
+CREATE POLICY p1 ON document FOR SELECT USING (true);
+-- one may insert documents only authored by them
+CREATE POLICY p2 ON document FOR INSERT WITH CHECK (dauthor = current_user);
+-- one may only update documents in 'novel' category
+CREATE POLICY p3 ON document FOR UPDATE
+  USING (cid = (SELECT cid from category WHERE cname = 'novel'))
+  WITH CHECK (dauthor = current_user);
+-- one may only delete documents in 'manga' category
+CREATE POLICY p4 ON document FOR DELETE
+  USING (cid = (SELECT cid from category WHERE cname = 'manga'));
+SELECT * FROM document;
+ did | cid | dlevel |      dauthor      |              dtitle              | dnotes 
+-----+-----+--------+-------------------+----------------------------------+--------
+   1 |  11 |      1 | regress_rls_bob   | my first novel                   | 
+   3 |  22 |      2 | regress_rls_bob   | my science fiction               | 
+   4 |  44 |      1 | regress_rls_bob   | my first manga                   | 
+   5 |  44 |      2 | regress_rls_bob   | my second manga                  | 
+   6 |  22 |      1 | regress_rls_carol | great science fiction            | 
+   7 |  33 |      2 | regress_rls_carol | great technology book            | 
+   8 |  44 |      1 | regress_rls_carol | great manga                      | 
+   9 |  22 |      1 | regress_rls_dave  | awesome science fiction          | 
+  10 |  33 |      2 | regress_rls_dave  | awesome technology book          | 
+  11 |  33 |      1 | regress_rls_carol | hoge                             | 
+  33 |  22 |      1 | regress_rls_bob   | okay science fiction             | 
+   2 |  11 |      2 | regress_rls_bob   | my first novel                   | 
+  78 |  33 |      1 | regress_rls_bob   | some technology novel            | 
+  79 |  33 |      1 | regress_rls_bob   | technology book, can only insert | 
+(14 rows)
+
+SET SESSION AUTHORIZATION regress_rls_bob;
+-- Fails, since update violates WITH CHECK qual on dauthor
+MERGE INTO document d
+USING (SELECT 1 as sdid) s
+ON did = s.sdid
+WHEN MATCHED THEN
+	UPDATE SET dnotes = dnotes || ' notes added by merge1 ', dauthor = 'regress_rls_alice';
+ERROR:  new row violates row-level security policy for table "document"
+-- Should be OK since USING and WITH CHECK quals pass
+MERGE INTO document d
+USING (SELECT 1 as sdid) s
+ON did = s.sdid
+WHEN MATCHED THEN
+	UPDATE SET dnotes = dnotes || ' notes added by merge2 ';
+-- Even when dauthor is updated explicitly, but to the existing value
+MERGE INTO document d
+USING (SELECT 1 as sdid) s
+ON did = s.sdid
+WHEN MATCHED THEN
+	UPDATE SET dnotes = dnotes || ' notes added by merge3 ', dauthor = 'regress_rls_bob';
+-- There is a MATCH for did = 3, but UPDATE's USING qual does not allow
+-- updating an item in category 'science fiction'
+MERGE INTO document d
+USING (SELECT 3 as sdid) s
+ON did = s.sdid
+WHEN MATCHED THEN
+	UPDATE SET dnotes = dnotes || ' notes added by merge ';
+ERROR:  target row violates row-level security policy (USING expression) for table "document"
+-- The same thing with DELETE action, but fails again because no permissions
+-- to delete items in 'science fiction' category that did 3 belongs to.
+MERGE INTO document d
+USING (SELECT 3 as sdid) s
+ON did = s.sdid
+WHEN MATCHED THEN
+	DELETE;
+ERROR:  target row violates row-level security policy (USING expression) for table "document"
+-- Document with did 4 belongs to 'manga' category which is allowed for
+-- deletion. But this fails because the UPDATE action is matched first and
+-- UPDATE policy does not allow updation in the category.
+MERGE INTO document d
+USING (SELECT 4 as sdid) s
+ON did = s.sdid
+WHEN MATCHED AND dnotes = '' THEN
+	UPDATE SET dnotes = dnotes || ' notes added by merge '
+WHEN MATCHED THEN
+	DELETE;
+ERROR:  target row violates row-level security policy (USING expression) for table "document"
+-- UPDATE action is not matched this time because of the WHEN AND qual.
+-- DELETE still fails because role regress_rls_bob does not have SELECT
+-- privileges on 'manga' category row in the category table.
+MERGE INTO document d
+USING (SELECT 4 as sdid) s
+ON did = s.sdid
+WHEN MATCHED AND dnotes <> '' THEN
+	UPDATE SET dnotes = dnotes || ' notes added by merge '
+WHEN MATCHED THEN
+	DELETE;
+ERROR:  target row violates row-level security policy (USING expression) for table "document"
+SELECT * FROM document WHERE did = 4;
+ did | cid | dlevel |     dauthor     |     dtitle     | dnotes 
+-----+-----+--------+-----------------+----------------+--------
+   4 |  44 |      1 | regress_rls_bob | my first manga | 
+(1 row)
+
+-- Switch to regress_rls_carol role and try the DELETE again. It should succeed
+-- this time
+RESET SESSION AUTHORIZATION;
+SET SESSION AUTHORIZATION regress_rls_carol;
+MERGE INTO document d
+USING (SELECT 4 as sdid) s
+ON did = s.sdid
+WHEN MATCHED AND dnotes <> '' THEN
+	UPDATE SET dnotes = dnotes || ' notes added by merge '
+WHEN MATCHED THEN
+	DELETE;
+-- Switch back to regress_rls_bob role
+RESET SESSION AUTHORIZATION;
+SET SESSION AUTHORIZATION regress_rls_bob;
+-- Try INSERT action. This fails because we are trying to insert
+-- dauthor = regress_rls_dave and INSERT's WITH CHECK does not allow
+-- that
+MERGE INTO document d
+USING (SELECT 12 as sdid) s
+ON did = s.sdid
+WHEN MATCHED THEN
+	DELETE
+WHEN NOT MATCHED THEN
+	INSERT VALUES (12, 11, 1, 'regress_rls_dave', 'another novel');
+ERROR:  new row violates row-level security policy for table "document"
+-- This should be fine
+MERGE INTO document d
+USING (SELECT 12 as sdid) s
+ON did = s.sdid
+WHEN MATCHED THEN
+	DELETE
+WHEN NOT MATCHED THEN
+	INSERT VALUES (12, 11, 1, 'regress_rls_bob', 'another novel');
+-- ok
+MERGE INTO document d
+USING (SELECT 1 as sdid) s
+ON did = s.sdid
+WHEN MATCHED THEN
+	UPDATE SET dnotes = dnotes || ' notes added by merge4 '
+WHEN NOT MATCHED THEN
+	INSERT VALUES (12, 11, 1, 'regress_rls_bob', 'another novel');
+-- drop and create a new SELECT policy which prevents us from reading
+-- any document except with category 'magna'
+RESET SESSION AUTHORIZATION;
+DROP POLICY p1 ON document;
+CREATE POLICY p1 ON document FOR SELECT
+  USING (cid = (SELECT cid from category WHERE cname = 'manga'));
+SET SESSION AUTHORIZATION regress_rls_bob;
+-- MERGE can no longer see the matching row and hence attempts the
+-- NOT MATCHED action, which results in unique key violation
+MERGE INTO document d
+USING (SELECT 1 as sdid) s
+ON did = s.sdid
+WHEN MATCHED THEN
+	UPDATE SET dnotes = dnotes || ' notes added by merge5 '
+WHEN NOT MATCHED THEN
+	INSERT VALUES (12, 11, 1, 'regress_rls_bob', 'another novel');
+ERROR:  duplicate key value violates unique constraint "document_pkey"
+RESET SESSION AUTHORIZATION;
+-- drop the restrictive SELECT policy so that we can look at the
+-- final state of the table
+DROP POLICY p1 ON document;
+-- Just check everything went per plan
+SELECT * FROM document;
+ did | cid | dlevel |      dauthor      |              dtitle              |                                dnotes                                 
+-----+-----+--------+-------------------+----------------------------------+-----------------------------------------------------------------------
+   3 |  22 |      2 | regress_rls_bob   | my science fiction               | 
+   5 |  44 |      2 | regress_rls_bob   | my second manga                  | 
+   6 |  22 |      1 | regress_rls_carol | great science fiction            | 
+   7 |  33 |      2 | regress_rls_carol | great technology book            | 
+   8 |  44 |      1 | regress_rls_carol | great manga                      | 
+   9 |  22 |      1 | regress_rls_dave  | awesome science fiction          | 
+  10 |  33 |      2 | regress_rls_dave  | awesome technology book          | 
+  11 |  33 |      1 | regress_rls_carol | hoge                             | 
+  33 |  22 |      1 | regress_rls_bob   | okay science fiction             | 
+   2 |  11 |      2 | regress_rls_bob   | my first novel                   | 
+  78 |  33 |      1 | regress_rls_bob   | some technology novel            | 
+  79 |  33 |      1 | regress_rls_bob   | technology book, can only insert | 
+  12 |  11 |      1 | regress_rls_bob   | another novel                    | 
+   1 |  11 |      1 | regress_rls_bob   | my first novel                   |  notes added by merge2  notes added by merge3  notes added by merge4 
+(14 rows)
+
 --
 -- ROLE/GROUP
 --
diff --git a/src/test/regress/expected/rules.out b/src/test/regress/expected/rules.out
index 735dd37acf..8e08102f95 100644
--- a/src/test/regress/expected/rules.out
+++ b/src/test/regress/expected/rules.out
@@ -3265,6 +3265,37 @@ CREATE RULE rules_parted_table_insert AS ON INSERT to rules_parted_table
 ALTER RULE rules_parted_table_insert ON rules_parted_table RENAME TO rules_parted_table_insert_redirect;
 DROP TABLE rules_parted_table;
 --
+-- test MERGE
+--
+CREATE TABLE rule_merge1 (a int, b text);
+CREATE TABLE rule_merge2 (a int, b text);
+CREATE RULE rule1 AS ON INSERT TO rule_merge1
+	DO INSTEAD INSERT INTO rule_merge2 VALUES (NEW.*);
+CREATE RULE rule2 AS ON UPDATE TO rule_merge1
+	DO INSTEAD UPDATE rule_merge2 SET a = NEW.a, b = NEW.b
+	WHERE a = OLD.a;
+CREATE RULE rule3 AS ON DELETE TO rule_merge1
+	DO INSTEAD DELETE FROM rule_merge2 WHERE a = OLD.a;
+-- MERGE not supported for table with rules
+MERGE INTO rule_merge1 t USING (SELECT 1 AS a) s
+	ON t.a = s.a
+	WHEN MATCHED AND t.a < 2 THEN
+		UPDATE SET b = b || ' updated by merge'
+	WHEN MATCHED AND t.a > 2 THEN
+		DELETE
+	WHEN NOT MATCHED THEN
+		INSERT VALUES (s.a, '');
+ERROR:  MERGE is not supported for relations with rules
+-- should be ok with the other table though
+MERGE INTO rule_merge2 t USING (SELECT 1 AS a) s
+	ON t.a = s.a
+	WHEN MATCHED AND t.a < 2 THEN
+		UPDATE SET b = b || ' updated by merge'
+	WHEN MATCHED AND t.a > 2 THEN
+		DELETE
+	WHEN NOT MATCHED THEN
+		INSERT VALUES (s.a, '');
+--
 -- Test enabling/disabling
 --
 CREATE TABLE ruletest1 (a int);
diff --git a/src/test/regress/expected/triggers.out b/src/test/regress/expected/triggers.out
index c62f88c169..c92fe4dfbe 100644
--- a/src/test/regress/expected/triggers.out
+++ b/src/test/regress/expected/triggers.out
@@ -2772,6 +2772,54 @@ delete from self_ref where a = 1;
 NOTICE:  trigger_func(self_ref) called: action = DELETE, when = BEFORE, level = STATEMENT
 NOTICE:  trigger = self_ref_s_trig, old table = (1,), (2,1), (3,2), (4,3)
 drop table self_ref;
+--
+-- test transition tables with MERGE
+--
+create table merge_target_table (a int primary key, b text);
+create trigger merge_target_table_insert_trig
+  after insert on merge_target_table referencing new table as new_table
+  for each statement execute procedure dump_insert();
+create trigger merge_target_table_update_trig
+  after update on merge_target_table referencing old table as old_table new table as new_table
+  for each statement execute procedure dump_update();
+create trigger merge_target_table_delete_trig
+  after delete on merge_target_table referencing old table as old_table
+  for each statement execute procedure dump_delete();
+create table merge_source_table (a int, b text);
+insert into merge_source_table
+  values (1, 'initial1'), (2, 'initial2'),
+		 (3, 'initial3'), (4, 'initial4');
+merge into merge_target_table t
+using merge_source_table s
+on t.a = s.a
+when not matched then
+  insert values (a, b);
+NOTICE:  trigger = merge_target_table_insert_trig, new table = (1,initial1), (2,initial2), (3,initial3), (4,initial4)
+merge into merge_target_table t
+using merge_source_table s
+on t.a = s.a
+when matched and s.a <= 2 then
+	update set b = t.b || ' updated by merge'
+when matched and s.a > 2 then
+	delete
+when not matched then
+  insert values (a, b);
+NOTICE:  trigger = merge_target_table_delete_trig, old table = (3,initial3), (4,initial4)
+NOTICE:  trigger = merge_target_table_update_trig, old table = (1,initial1), (2,initial2), new table = (1,"initial1 updated by merge"), (2,"initial2 updated by merge")
+NOTICE:  trigger = merge_target_table_insert_trig, new table = <NULL>
+merge into merge_target_table t
+using merge_source_table s
+on t.a = s.a
+when matched and s.a <= 2 then
+	update set b = t.b || ' updated again by merge'
+when matched and s.a > 2 then
+	delete
+when not matched then
+  insert values (a, b);
+NOTICE:  trigger = merge_target_table_delete_trig, old table = <NULL>
+NOTICE:  trigger = merge_target_table_update_trig, old table = (1,"initial1 updated by merge"), (2,"initial2 updated by merge"), new table = (1,"initial1 updated by merge updated again by merge"), (2,"initial2 updated by merge updated again by merge")
+NOTICE:  trigger = merge_target_table_insert_trig, new table = (3,initial3), (4,initial4)
+drop table merge_source_table, merge_target_table;
 -- cleanup
 drop function dump_insert();
 drop function dump_update();
diff --git a/src/test/regress/expected/with.out b/src/test/regress/expected/with.out
index 2a2085556b..350a34d987 100644
--- a/src/test/regress/expected/with.out
+++ b/src/test/regress/expected/with.out
@@ -1904,6 +1904,143 @@ RETURNING k, v;
 (0 rows)
 
 DROP TABLE withz;
+-- WITH referenced by MERGE statement
+CREATE TABLE m AS SELECT i AS k, (i || ' v')::text v FROM generate_series(1, 16, 3) i;
+ALTER TABLE m ADD UNIQUE (k);
+WITH RECURSIVE cte_basic AS (SELECT 1 a, 'cte_basic val' b)
+MERGE INTO m USING (select 0 k, 'merge source SubPlan' v) o ON m.k=o.k
+WHEN MATCHED THEN UPDATE SET v = (SELECT b || ' merge update' FROM cte_basic WHERE cte_basic.a = m.k LIMIT 1)
+WHEN NOT MATCHED THEN INSERT VALUES(o.k, o.v);
+ERROR:  WITH RECURSIVE is not supported for MERGE statement
+-- Basic:
+WITH cte_basic AS (SELECT 1 a, 'cte_basic val' b)
+MERGE INTO m USING (select 0 k, 'merge source SubPlan' v) o ON m.k=o.k
+WHEN MATCHED THEN UPDATE SET v = (SELECT b || ' merge update' FROM cte_basic WHERE cte_basic.a = m.k LIMIT 1)
+WHEN NOT MATCHED THEN INSERT VALUES(o.k, o.v);
+-- Examine
+SELECT * FROM m where k = 0;
+ k |          v           
+---+----------------------
+ 0 | merge source SubPlan
+(1 row)
+
+-- See EXPLAIN output for same query:
+EXPLAIN (VERBOSE, COSTS OFF)
+WITH cte_basic AS (SELECT 1 a, 'cte_basic val' b)
+MERGE INTO m USING (select 0 k, 'merge source SubPlan' v) o ON m.k=o.k
+WHEN MATCHED THEN UPDATE SET v = (SELECT b || ' merge update' FROM cte_basic WHERE cte_basic.a = m.k LIMIT 1)
+WHEN NOT MATCHED THEN INSERT VALUES(o.k, o.v);
+                            QUERY PLAN                             
+-------------------------------------------------------------------
+ Merge on public.m
+   CTE cte_basic
+     ->  Result
+           Output: 1, 'cte_basic val'::text
+   ->  Hash Right Join
+         Output: o.k, o.v, o.*, m_1.ctid
+         Hash Cond: (m_1.k = o.k)
+         ->  Seq Scan on public.m m_1
+               Output: m_1.ctid, m_1.k
+         ->  Hash
+               Output: o.k, o.v, o.*
+               ->  Subquery Scan on o
+                     Output: o.k, o.v, o.*
+                     ->  Result
+                           Output: 0, 'merge source SubPlan'::text
+   SubPlan 2
+     ->  Limit
+           Output: ((cte_basic.b || ' merge update'::text))
+           ->  CTE Scan on cte_basic
+                 Output: (cte_basic.b || ' merge update'::text)
+                 Filter: (cte_basic.a = m.k)
+(21 rows)
+
+-- InitPlan
+WITH cte_init AS (SELECT 1 a, 'cte_init val' b)
+MERGE INTO m USING (select 1 k, 'merge source InitPlan' v) o ON m.k=o.k
+WHEN MATCHED THEN UPDATE SET v = (SELECT b || ' merge update' FROM cte_init WHERE a = 1 LIMIT 1)
+WHEN NOT MATCHED THEN INSERT VALUES(o.k, o.v);
+-- Examine
+SELECT * FROM m where k = 1;
+ k |             v             
+---+---------------------------
+ 1 | cte_init val merge update
+(1 row)
+
+-- See EXPLAIN output for same query:
+EXPLAIN (VERBOSE, COSTS OFF)
+WITH cte_init AS (SELECT 1 a, 'cte_init val' b)
+MERGE INTO m USING (select 1 k, 'merge source InitPlan' v) o ON m.k=o.k
+WHEN MATCHED THEN UPDATE SET v = (SELECT b || ' merge update' FROM cte_init WHERE a = 1 LIMIT 1)
+WHEN NOT MATCHED THEN INSERT VALUES(o.k, o.v);
+                             QUERY PLAN                             
+--------------------------------------------------------------------
+ Merge on public.m
+   CTE cte_init
+     ->  Result
+           Output: 1, 'cte_init val'::text
+   InitPlan 2 (returns $1)
+     ->  Limit
+           Output: ((cte_init.b || ' merge update'::text))
+           ->  CTE Scan on cte_init
+                 Output: (cte_init.b || ' merge update'::text)
+                 Filter: (cte_init.a = 1)
+   ->  Hash Right Join
+         Output: o.k, o.v, o.*, m_1.ctid
+         Hash Cond: (m_1.k = o.k)
+         ->  Seq Scan on public.m m_1
+               Output: m_1.ctid, m_1.k
+         ->  Hash
+               Output: o.k, o.v, o.*
+               ->  Subquery Scan on o
+                     Output: o.k, o.v, o.*
+                     ->  Result
+                           Output: 1, 'merge source InitPlan'::text
+(21 rows)
+
+-- MERGE source comes from CTE:
+WITH merge_source_cte AS (SELECT 15 a, 'merge_source_cte val' b)
+MERGE INTO m USING (select * from merge_source_cte) o ON m.k=o.a
+WHEN MATCHED THEN UPDATE SET v = (SELECT b || merge_source_cte.*::text || ' merge update' FROM merge_source_cte WHERE a = 15)
+WHEN NOT MATCHED THEN INSERT VALUES(o.a, o.b || (SELECT merge_source_cte.*::text || ' merge insert' FROM merge_source_cte));
+-- Examine
+SELECT * FROM m where k = 15;
+ k  |                              v                               
+----+--------------------------------------------------------------
+ 15 | merge_source_cte val(15,"merge_source_cte val") merge insert
+(1 row)
+
+-- See EXPLAIN output for same query:
+EXPLAIN (VERBOSE, COSTS OFF)
+WITH merge_source_cte AS (SELECT 15 a, 'merge_source_cte val' b)
+MERGE INTO m USING (select * from merge_source_cte) o ON m.k=o.a
+WHEN MATCHED THEN UPDATE SET v = (SELECT b || merge_source_cte.*::text || ' merge update' FROM merge_source_cte WHERE a = 15)
+WHEN NOT MATCHED THEN INSERT VALUES(o.a, o.b || (SELECT merge_source_cte.*::text || ' merge insert' FROM merge_source_cte));
+                                                  QUERY PLAN                                                   
+---------------------------------------------------------------------------------------------------------------
+ Merge on public.m
+   CTE merge_source_cte
+     ->  Result
+           Output: 15, 'merge_source_cte val'::text
+   InitPlan 2 (returns $1)
+     ->  CTE Scan on merge_source_cte merge_source_cte_1
+           Output: ((merge_source_cte_1.b || (merge_source_cte_1.*)::text) || ' merge update'::text)
+           Filter: (merge_source_cte_1.a = 15)
+   InitPlan 3 (returns $2)
+     ->  CTE Scan on merge_source_cte merge_source_cte_2
+           Output: ((merge_source_cte_2.*)::text || ' merge insert'::text)
+   ->  Hash Right Join
+         Output: merge_source_cte.a, merge_source_cte.b, ROW(merge_source_cte.a, merge_source_cte.b), m_1.ctid
+         Hash Cond: (m_1.k = merge_source_cte.a)
+         ->  Seq Scan on public.m m_1
+               Output: m_1.ctid, m_1.k
+         ->  Hash
+               Output: merge_source_cte.a, merge_source_cte.b
+               ->  CTE Scan on merge_source_cte
+                     Output: merge_source_cte.a, merge_source_cte.b
+(20 rows)
+
+DROP TABLE m;
 -- check that run to completion happens in proper ordering
 TRUNCATE TABLE y;
 INSERT INTO y SELECT generate_series(1, 3);
diff --git a/src/test/regress/parallel_schedule b/src/test/regress/parallel_schedule
index cc0bbf5db9..97aa4dc259 100644
--- a/src/test/regress/parallel_schedule
+++ b/src/test/regress/parallel_schedule
@@ -84,7 +84,7 @@ test: select_into select_distinct select_distinct_on select_implicit select_havi
 # ----------
 # Another group of parallel tests
 # ----------
-test: brin gin gist spgist privileges init_privs security_label collate matview lock replica_identity rowsecurity object_address tablesample groupingsets drop_operator password
+test: brin gin gist spgist privileges init_privs security_label collate matview lock replica_identity rowsecurity object_address tablesample groupingsets drop_operator password merge
 
 # ----------
 # Another group of parallel tests
diff --git a/src/test/regress/serial_schedule b/src/test/regress/serial_schedule
index 0c10c7100c..dfcd54c7ba 100644
--- a/src/test/regress/serial_schedule
+++ b/src/test/regress/serial_schedule
@@ -120,6 +120,7 @@ test: tablesample
 test: groupingsets
 test: drop_operator
 test: password
+test: merge
 test: alter_generic
 test: alter_operator
 test: misc
diff --git a/src/test/regress/sql/identity.sql b/src/test/regress/sql/identity.sql
index a35f331f4e..f8f34eaf18 100644
--- a/src/test/regress/sql/identity.sql
+++ b/src/test/regress/sql/identity.sql
@@ -246,3 +246,48 @@ CREATE TABLE itest_child PARTITION OF itest_parent (
     f3 WITH OPTIONS GENERATED ALWAYS AS IDENTITY
 ) FOR VALUES FROM ('2016-07-01') TO ('2016-08-01'); -- error
 DROP TABLE itest_parent;
+
+-- MERGE tests
+CREATE TABLE itest14 (a int GENERATED ALWAYS AS IDENTITY, b text);
+CREATE TABLE itest15 (a int GENERATED BY DEFAULT AS IDENTITY, b text);
+
+MERGE INTO itest14 t
+USING (SELECT 10 AS s_a, 'inserted by merge' AS s_b) s
+ON t.a = s.s_a
+WHEN NOT MATCHED THEN
+	INSERT (a, b) VALUES (s.s_a, s.s_b);
+
+MERGE INTO itest14 t
+USING (SELECT 20 AS s_a, 'inserted by merge' AS s_b) s
+ON t.a = s.s_a
+WHEN NOT MATCHED THEN
+	INSERT (a, b) OVERRIDING USER VALUE VALUES (s.s_a, s.s_b);
+
+MERGE INTO itest14 t
+USING (SELECT 30 AS s_a, 'inserted by merge' AS s_b) s
+ON t.a = s.s_a
+WHEN NOT MATCHED THEN
+	INSERT (a, b) OVERRIDING SYSTEM VALUE VALUES (s.s_a, s.s_b);
+
+MERGE INTO itest15 t
+USING (SELECT 10 AS s_a, 'inserted by merge' AS s_b) s
+ON t.a = s.s_a
+WHEN NOT MATCHED THEN
+	INSERT (a, b) VALUES (s.s_a, s.s_b);
+
+MERGE INTO itest15 t
+USING (SELECT 20 AS s_a, 'inserted by merge' AS s_b) s
+ON t.a = s.s_a
+WHEN NOT MATCHED THEN
+	INSERT (a, b) OVERRIDING USER VALUE VALUES (s.s_a, s.s_b);
+
+MERGE INTO itest15 t
+USING (SELECT 30 AS s_a, 'inserted by merge' AS s_b) s
+ON t.a = s.s_a
+WHEN NOT MATCHED THEN
+	INSERT (a, b) OVERRIDING SYSTEM VALUE VALUES (s.s_a, s.s_b);
+
+SELECT * FROM itest14;
+SELECT * FROM itest15;
+DROP TABLE itest14;
+DROP TABLE itest15;
diff --git a/src/test/regress/sql/merge.sql b/src/test/regress/sql/merge.sql
new file mode 100644
index 0000000000..e5f87e7259
--- /dev/null
+++ b/src/test/regress/sql/merge.sql
@@ -0,0 +1,1165 @@
+--
+-- MERGE
+--
+--\set VERBOSITY verbose
+
+--set debug_print_rewritten = true;
+--set debug_print_parse = true;
+--set debug_print_pretty = true;
+
+
+CREATE USER merge_privs;
+CREATE USER merge_no_privs;
+DROP TABLE IF EXISTS target;
+DROP TABLE IF EXISTS source;
+CREATE TABLE target (tid integer, balance integer);
+CREATE TABLE source (sid integer, delta integer); --no index
+INSERT INTO target VALUES (1, 10);
+INSERT INTO target VALUES (2, 20);
+INSERT INTO target VALUES (3, 30);
+SELECT t.ctid is not null as matched, t.*, s.* FROM source s FULL OUTER JOIN target t ON s.sid = t.tid ORDER BY t.tid, s.sid;
+
+ALTER TABLE target OWNER TO merge_privs;
+ALTER TABLE source OWNER TO merge_privs;
+
+CREATE TABLE target2 (tid integer, balance integer);
+CREATE TABLE source2 (sid integer, delta integer);
+
+ALTER TABLE target2 OWNER TO merge_no_privs;
+ALTER TABLE source2 OWNER TO merge_no_privs;
+
+GRANT INSERT ON target TO merge_no_privs;
+
+SET SESSION AUTHORIZATION merge_privs;
+
+EXPLAIN (COSTS OFF)
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED THEN
+	DELETE
+;
+
+--
+-- Errors
+--
+MERGE INTO target t RANDOMWORD
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED THEN
+	UPDATE SET balance = 0
+;
+-- MATCHED/INSERT error
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED THEN
+	INSERT DEFAULT VALUES
+;
+-- incorrectly specifying INTO target
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT INTO target DEFAULT VALUES
+;
+-- Multiple VALUES clause
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT VALUES (1,1), (2,2);
+;
+-- SELECT query for INSERT
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT SELECT (1, 1);
+;
+-- NOT MATCHED/UPDATE
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	UPDATE SET balance = 0
+;
+-- UPDATE tablename
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED THEN
+	UPDATE target SET balance = 0
+;
+
+-- unsupported relation types
+-- view
+CREATE VIEW tv AS SELECT * FROM target;
+MERGE INTO tv t
+USING source s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT DEFAULT VALUES;
+DROP VIEW tv;
+
+-- materialized view
+CREATE MATERIALIZED VIEW mv AS SELECT * FROM target;
+MERGE INTO mv t
+USING source s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT DEFAULT VALUES;
+DROP MATERIALIZED VIEW mv;
+
+-- inherited table
+CREATE TABLE inhp (tid int, balance int);
+CREATE TABLE child1() INHERITS (inhp);
+CREATE TABLE child2() INHERITS (child1);
+
+MERGE INTO inhp t
+USING source s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT DEFAULT VALUES;
+
+MERGE INTO child1 t
+USING source s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT DEFAULT VALUES;
+
+-- this should be ok
+MERGE INTO child2 t
+USING source s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT DEFAULT VALUES;
+DROP TABLE inhp, child1, child2;
+
+-- permissions
+
+MERGE INTO target
+USING source2
+ON target.tid = source2.sid
+WHEN MATCHED THEN
+	UPDATE SET balance = 0
+;
+
+GRANT INSERT ON target TO merge_no_privs;
+SET SESSION AUTHORIZATION merge_no_privs;
+
+MERGE INTO target
+USING source2
+ON target.tid = source2.sid
+WHEN MATCHED THEN
+	UPDATE SET balance = 0
+;
+
+GRANT UPDATE ON target2 TO merge_privs;
+SET SESSION AUTHORIZATION merge_privs;
+
+MERGE INTO target2
+USING source
+ON target2.tid = source.sid
+WHEN MATCHED THEN
+	DELETE
+;
+
+MERGE INTO target2
+USING source
+ON target2.tid = source.sid
+WHEN NOT MATCHED THEN
+	INSERT DEFAULT VALUES
+;
+
+-- check if the target can be accessed from source relation subquery; we should
+-- not be able to do so
+MERGE INTO target t
+USING (SELECT * FROM source WHERE t.tid > sid) s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT DEFAULT VALUES
+;
+
+--
+-- initial tests
+--
+-- zero rows in source has no effect
+MERGE INTO target
+USING source
+ON target.tid = source.sid
+WHEN MATCHED THEN
+	UPDATE SET balance = 0
+;
+
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED THEN
+	UPDATE SET balance = 0
+;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED THEN
+	DELETE
+;
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT DEFAULT VALUES
+;
+ROLLBACK;
+
+-- insert some non-matching source rows to work from
+INSERT INTO source VALUES (4, 40);
+SELECT * FROM source ORDER BY sid;
+SELECT * FROM target ORDER BY tid;
+
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	DO NOTHING
+;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED THEN
+	UPDATE SET balance = 0
+;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED THEN
+	DELETE
+;
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT DEFAULT VALUES
+;
+SELECT * FROM target ORDER BY tid;
+ROLLBACK;
+
+-- index plans
+INSERT INTO target SELECT generate_series(1000,2500), 0;
+ALTER TABLE target ADD PRIMARY KEY (tid);
+ANALYZE target;
+
+EXPLAIN (COSTS OFF)
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED THEN
+	UPDATE SET balance = 0
+;
+EXPLAIN (COSTS OFF)
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED THEN
+	DELETE
+;
+EXPLAIN (COSTS OFF)
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT VALUES (4, NULL);
+;
+DELETE FROM target WHERE tid > 100;
+ANALYZE target;
+
+-- insert some matching source rows to work from
+INSERT INTO source VALUES (2, 5);
+INSERT INTO source VALUES (3, 20);
+SELECT * FROM source ORDER BY sid;
+SELECT * FROM target ORDER BY tid;
+
+-- equivalent of an UPDATE join
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED THEN
+	UPDATE SET balance = 0
+;
+SELECT * FROM target ORDER BY tid;
+ROLLBACK;
+
+-- equivalent of a DELETE join
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED THEN
+	DELETE
+;
+SELECT * FROM target ORDER BY tid;
+ROLLBACK;
+
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT VALUES (4, NULL)
+;
+SELECT * FROM target ORDER BY tid;
+ROLLBACK;
+
+-- duplicate source row causes multiple target row update ERROR
+INSERT INTO source VALUES (2, 5);
+SELECT * FROM source ORDER BY sid;
+SELECT * FROM target ORDER BY tid;
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED THEN
+	UPDATE SET balance = 0
+;
+ROLLBACK;
+
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED THEN
+	DELETE
+;
+ROLLBACK;
+
+-- correct source data
+DELETE FROM source WHERE sid = 2;
+INSERT INTO source VALUES (2, 5);
+SELECT * FROM source ORDER BY sid;
+SELECT * FROM target ORDER BY tid;
+
+-- remove constraints
+alter table target drop CONSTRAINT target_pkey;
+alter table target alter column tid drop not null;
+
+-- multiple actions
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT VALUES (4, 4)
+WHEN MATCHED THEN
+	UPDATE SET balance = 0
+;
+SELECT * FROM target ORDER BY tid;
+ROLLBACK;
+
+-- should be equivalent
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED THEN
+	INSERT VALUES (4, 4);
+;
+SELECT * FROM target ORDER BY tid;
+ROLLBACK;
+
+-- column references
+-- do a simple equivalent of an UPDATE join
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED THEN
+	UPDATE SET balance = t.balance + s.delta
+;
+SELECT * FROM target ORDER BY tid;
+ROLLBACK;
+
+-- do a simple equivalent of an INSERT SELECT
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT VALUES (s.sid, s.delta)
+;
+SELECT * FROM target ORDER BY tid;
+ROLLBACK;
+
+-- and again with explicitly identified column list
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT (tid, balance) VALUES (s.sid, s.delta)
+;
+SELECT * FROM target ORDER BY tid;
+ROLLBACK;
+
+-- and again with a subtle error: referring to non-existent target row for NOT MATCHED
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT (tid, balance) VALUES (t.tid, s.delta)
+;
+
+-- and again with a constant ON clause
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON (SELECT true)
+WHEN NOT MATCHED THEN
+	INSERT (tid, balance) VALUES (t.tid, s.delta)
+;
+SELECT * FROM target ORDER BY tid;
+ROLLBACK;
+
+-- now the classic UPSERT
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED THEN
+	UPDATE SET balance = t.balance + s.delta
+WHEN NOT MATCHED THEN
+	INSERT VALUES (s.sid, s.delta)
+;
+SELECT * FROM target ORDER BY tid;
+ROLLBACK;
+
+-- unreachable WHEN clause should ERROR
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED THEN /* Terminal WHEN clause for MATCHED */
+	DELETE
+WHEN MATCHED AND s.delta > 0 THEN
+	UPDATE SET balance = t.balance - s.delta
+;
+ROLLBACK;
+
+-- conditional WHEN clause
+CREATE TABLE wq_target (tid integer not null, balance integer DEFAULT -1);
+CREATE TABLE wq_source (balance integer, sid integer);
+
+INSERT INTO wq_source (sid, balance) VALUES (1, 100);
+
+BEGIN;
+-- try a simple INSERT with default values first
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT (tid) VALUES (s.sid);
+SELECT * FROM wq_target;
+ROLLBACK;
+
+-- this time with a FALSE condition
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED AND FALSE THEN
+	INSERT (tid) VALUES (s.sid);
+SELECT * FROM wq_target;
+
+-- this time with an actual condition which returns false
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED AND s.balance <> 100 THEN
+	INSERT (tid) VALUES (s.sid);
+SELECT * FROM wq_target;
+
+BEGIN;
+-- and now with a condition which returns true
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED AND s.balance = 100 THEN
+	INSERT (tid) VALUES (s.sid);
+SELECT * FROM wq_target;
+ROLLBACK;
+
+-- conditions in the NOT MATCHED clause can only refer to source columns
+BEGIN;
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED AND t.balance = 100 THEN
+	INSERT (tid) VALUES (s.sid);
+SELECT * FROM wq_target;
+ROLLBACK;
+
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED AND s.balance = 100 THEN
+	INSERT (tid) VALUES (s.sid);
+SELECT * FROM wq_target;
+
+-- conditions in MATCHED clause can refer to both source and target
+SELECT * FROM wq_source;
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN MATCHED AND s.balance = 100 THEN
+	UPDATE SET balance = t.balance + s.balance;
+SELECT * FROM wq_target;
+
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN MATCHED AND t.balance = 100 THEN
+	UPDATE SET balance = t.balance + s.balance;
+SELECT * FROM wq_target;
+
+-- check if AND works
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN MATCHED AND t.balance = 99 AND s.balance > 100 THEN
+	UPDATE SET balance = t.balance + s.balance;
+SELECT * FROM wq_target;
+
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN MATCHED AND t.balance = 99 AND s.balance = 100 THEN
+	UPDATE SET balance = t.balance + s.balance;
+SELECT * FROM wq_target;
+
+-- check if OR works
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN MATCHED AND t.balance = 99 OR s.balance > 100 THEN
+	UPDATE SET balance = t.balance + s.balance;
+SELECT * FROM wq_target;
+
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN MATCHED AND t.balance = 199 OR s.balance > 100 THEN
+	UPDATE SET balance = t.balance + s.balance;
+SELECT * FROM wq_target;
+
+-- check if subqueries work in the conditions?
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN MATCHED AND t.balance > (SELECT max(balance) FROM target) THEN
+	UPDATE SET balance = t.balance + s.balance;
+
+-- check if we can access system columns in the conditions
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN MATCHED AND t.xmin = t.xmax THEN
+	UPDATE SET balance = t.balance + s.balance;
+
+-- test preventing WHEN AND conditions from writing to the database
+create or replace function merge_when_and_write() returns boolean
+language plpgsql as
+$$
+BEGIN
+	INSERT INTO target VALUES (100, 100);
+	RETURN TRUE;
+END;
+$$;
+
+BEGIN;
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN MATCHED AND (merge_when_and_write()) THEN
+	UPDATE SET balance = t.balance + s.balance;
+ROLLBACK;
+drop function merge_when_and_write();
+
+DROP TABLE wq_target, wq_source;
+
+-- test triggers
+create or replace function merge_trigfunc () returns trigger
+language plpgsql as
+$$
+BEGIN
+	RAISE NOTICE '% % % trigger', TG_WHEN, TG_OP, TG_LEVEL;
+	IF (TG_WHEN = 'BEFORE' AND TG_LEVEL = 'ROW') THEN
+		IF (TG_OP = 'DELETE') THEN
+			RETURN OLD;
+		ELSE
+			RETURN NEW;
+		END IF;
+	ELSE
+		RETURN NULL;
+	END IF;
+END;
+$$;
+CREATE TRIGGER merge_bsi BEFORE INSERT ON target FOR EACH STATEMENT EXECUTE PROCEDURE merge_trigfunc ();
+CREATE TRIGGER merge_bsu BEFORE UPDATE ON target FOR EACH STATEMENT EXECUTE PROCEDURE merge_trigfunc ();
+CREATE TRIGGER merge_bsd BEFORE DELETE ON target FOR EACH STATEMENT EXECUTE PROCEDURE merge_trigfunc ();
+CREATE TRIGGER merge_asi AFTER INSERT ON target FOR EACH STATEMENT EXECUTE PROCEDURE merge_trigfunc ();
+CREATE TRIGGER merge_asu AFTER UPDATE ON target FOR EACH STATEMENT EXECUTE PROCEDURE merge_trigfunc ();
+CREATE TRIGGER merge_asd AFTER DELETE ON target FOR EACH STATEMENT EXECUTE PROCEDURE merge_trigfunc ();
+CREATE TRIGGER merge_bri BEFORE INSERT ON target FOR EACH ROW EXECUTE PROCEDURE merge_trigfunc ();
+CREATE TRIGGER merge_bru BEFORE UPDATE ON target FOR EACH ROW EXECUTE PROCEDURE merge_trigfunc ();
+CREATE TRIGGER merge_brd BEFORE DELETE ON target FOR EACH ROW EXECUTE PROCEDURE merge_trigfunc ();
+CREATE TRIGGER merge_ari AFTER INSERT ON target FOR EACH ROW EXECUTE PROCEDURE merge_trigfunc ();
+CREATE TRIGGER merge_aru AFTER UPDATE ON target FOR EACH ROW EXECUTE PROCEDURE merge_trigfunc ();
+CREATE TRIGGER merge_ard AFTER DELETE ON target FOR EACH ROW EXECUTE PROCEDURE merge_trigfunc ();
+
+-- now the classic UPSERT, with a DELETE
+BEGIN;
+UPDATE target SET balance = 0 WHERE tid = 3;
+--EXPLAIN (ANALYZE ON, COSTS OFF, SUMMARY OFF, TIMING OFF)
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED AND t.balance > s.delta THEN
+	UPDATE SET balance = t.balance - s.delta
+WHEN MATCHED THEN
+	DELETE
+WHEN NOT MATCHED THEN
+	INSERT VALUES (s.sid, s.delta)
+;
+SELECT * FROM target ORDER BY tid;
+ROLLBACK;
+
+-- test from PL/pgSQL
+-- make sure MERGE INTO isn't interpreted to mean returning variables like SELECT INTO
+BEGIN;
+DO LANGUAGE plpgsql $$
+BEGIN
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED AND t.balance > s.delta THEN
+	UPDATE SET balance = t.balance - s.delta
+;
+END;
+$$;
+ROLLBACK;
+
+--source constants
+BEGIN;
+MERGE INTO target t
+USING (SELECT 9 AS sid, 57 AS delta) AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT (tid, balance) VALUES (s.sid, s.delta)
+;
+SELECT * FROM target ORDER BY tid;
+ROLLBACK;
+
+--source query
+BEGIN;
+MERGE INTO target t
+USING (SELECT sid, delta FROM source WHERE delta > 0) AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT (tid, balance) VALUES (s.sid, s.delta)
+;
+SELECT * FROM target ORDER BY tid;
+ROLLBACK;
+
+BEGIN;
+MERGE INTO target t
+USING (SELECT sid, delta as newname FROM source WHERE delta > 0) AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT (tid, balance) VALUES (s.sid, s.newname)
+;
+SELECT * FROM target ORDER BY tid;
+ROLLBACK;
+
+--self-merge
+BEGIN;
+MERGE INTO target t1
+USING target t2
+ON t1.tid = t2.tid
+WHEN MATCHED THEN
+	UPDATE SET balance = t1.balance + t2.balance
+WHEN NOT MATCHED THEN
+	INSERT VALUES (t2.tid, t2.balance)
+;
+SELECT * FROM target ORDER BY tid;
+ROLLBACK;
+
+BEGIN;
+MERGE INTO target t
+USING (SELECT tid as sid, balance as delta FROM target WHERE balance > 0) AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT (tid, balance) VALUES (s.sid, s.delta)
+;
+SELECT * FROM target ORDER BY tid;
+ROLLBACK;
+
+BEGIN;
+MERGE INTO target t
+USING
+(SELECT sid, max(delta) AS delta
+ FROM source
+ GROUP BY sid
+ HAVING count(*) = 1
+ ORDER BY sid ASC) AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT (tid, balance) VALUES (s.sid, s.delta)
+;
+SELECT * FROM target ORDER BY tid;
+ROLLBACK;
+
+-- plpgsql parameters and results
+BEGIN;
+CREATE FUNCTION merge_func (p_id integer, p_bal integer)
+RETURNS INTEGER
+LANGUAGE plpgsql
+AS $$
+DECLARE
+ result integer;
+BEGIN
+MERGE INTO target t
+USING (SELECT p_id AS sid) AS s
+ON t.tid = s.sid
+WHEN MATCHED THEN
+	UPDATE SET balance = t.balance - p_bal
+;
+IF FOUND THEN
+	GET DIAGNOSTICS result := ROW_COUNT;
+END IF;
+RETURN result;
+END;
+$$;
+SELECT merge_func(3, 4);
+SELECT * FROM target ORDER BY tid;
+ROLLBACK;
+
+-- PREPARE
+BEGIN;
+prepare foom as merge into target t using (select 1 as sid) s on (t.tid = s.sid) when matched then update set balance = 1;
+execute foom;
+SELECT * FROM target ORDER BY tid;
+ROLLBACK;
+
+BEGIN;
+PREPARE foom2 (integer, integer) AS
+MERGE INTO target t
+USING (SELECT 1) s
+ON t.tid = $1
+WHEN MATCHED THEN
+UPDATE SET balance = $2;
+--EXPLAIN (ANALYZE ON, COSTS OFF, SUMMARY OFF, TIMING OFF)
+execute foom2 (1, 1);
+SELECT * FROM target ORDER BY tid;
+ROLLBACK;
+
+-- subqueries in source relation
+
+CREATE TABLE sq_target (tid integer NOT NULL, balance integer);
+CREATE TABLE sq_source (delta integer, sid integer, balance integer DEFAULT 0);
+
+INSERT INTO sq_target(tid, balance) VALUES (1,100), (2,200), (3,300);
+INSERT INTO sq_source(sid, delta) VALUES (1,10), (2,20), (4,40);
+
+BEGIN;
+MERGE INTO sq_target t
+USING (SELECT * FROM sq_source) s
+ON tid = sid
+WHEN MATCHED AND t.balance > delta THEN
+	UPDATE SET balance = t.balance + delta;
+SELECT * FROM sq_target;
+ROLLBACK;
+
+-- try a view
+CREATE VIEW v AS SELECT * FROM sq_source WHERE sid < 2;
+
+BEGIN;
+MERGE INTO sq_target
+USING v
+ON tid = sid
+WHEN MATCHED THEN
+    UPDATE SET balance = v.balance + delta;
+SELECT * FROM sq_target;
+ROLLBACK;
+
+-- ambiguous reference to a column
+BEGIN;
+MERGE INTO sq_target
+USING v
+ON tid = sid
+WHEN MATCHED AND tid > 2 THEN
+    UPDATE SET balance = balance + delta
+WHEN NOT MATCHED THEN
+	INSERT (balance, tid) VALUES (balance + delta, sid)
+WHEN MATCHED AND tid < 2 THEN
+	DELETE;
+ROLLBACK;
+
+BEGIN;
+INSERT INTO sq_source (sid, balance, delta) VALUES (-1, -1, -10);
+MERGE INTO sq_target t
+USING v
+ON tid = sid
+WHEN MATCHED AND tid > 2 THEN
+    UPDATE SET balance = t.balance + delta
+WHEN NOT MATCHED THEN
+	INSERT (balance, tid) VALUES (balance + delta, sid)
+WHEN MATCHED AND tid < 2 THEN
+	DELETE;
+SELECT * FROM sq_target;
+ROLLBACK;
+
+-- CTEs
+BEGIN;
+INSERT INTO sq_source (sid, balance, delta) VALUES (-1, -1, -10);
+WITH targq AS (
+	SELECT * FROM v
+)
+MERGE INTO sq_target t
+USING v
+ON tid = sid
+WHEN MATCHED AND tid > 2 THEN
+    UPDATE SET balance = t.balance + delta
+WHEN NOT MATCHED THEN
+	INSERT (balance, tid) VALUES (balance + delta, sid)
+WHEN MATCHED AND tid < 2 THEN
+	DELETE
+;
+ROLLBACK;
+
+-- RETURNING
+BEGIN;
+INSERT INTO sq_source (sid, balance, delta) VALUES (-1, -1, -10);
+MERGE INTO sq_target t
+USING v
+ON tid = sid
+WHEN MATCHED AND tid > 2 THEN
+    UPDATE SET balance = t.balance + delta
+WHEN NOT MATCHED THEN
+	INSERT (balance, tid) VALUES (balance + delta, sid)
+WHEN MATCHED AND tid < 2 THEN
+	DELETE
+RETURNING *
+;
+ROLLBACK;
+
+-- EXPLAIN
+CREATE TABLE ex_mtarget (a int, b int);
+CREATE TABLE ex_msource (a int, b int);
+INSERT INTO ex_mtarget SELECT i, i*10 FROM generate_series(1,100,2) i;
+INSERT INTO ex_msource SELECT i, i*10 FROM generate_series(1,100,1) i;
+
+-- only updates
+--EXPLAIN (ANALYZE ON, COSTS OFF, SUMMARY OFF, TIMING OFF)
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN MATCHED THEN
+	UPDATE SET b = t.b + 1;
+
+-- only updates to selected tuples
+--EXPLAIN (ANALYZE ON, COSTS OFF, SUMMARY OFF, TIMING OFF)
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN MATCHED AND t.a < 10 THEN
+	UPDATE SET b = t.b + 1;
+
+-- updates + deletes
+--EXPLAIN (ANALYZE ON, COSTS OFF, SUMMARY OFF, TIMING OFF)
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN MATCHED AND t.a < 10 THEN
+	UPDATE SET b = t.b + 1
+WHEN MATCHED AND t.a >= 10 AND t.a <= 20 THEN
+	DELETE;
+
+-- only inserts
+--EXPLAIN (ANALYZE ON, COSTS OFF, SUMMARY OFF, TIMING OFF)
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED AND s.a < 10 THEN
+	INSERT VALUES (a, b);
+
+-- all three
+--EXPLAIN (ANALYZE ON, COSTS OFF, SUMMARY OFF, TIMING OFF)
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN MATCHED AND t.a < 10 THEN
+	UPDATE SET b = t.b + 1
+WHEN MATCHED AND t.a >= 30 AND t.a <= 40 THEN
+	DELETE
+WHEN NOT MATCHED AND s.a < 20 THEN
+	INSERT VALUES (a, b);
+
+DROP TABLE ex_msource, ex_mtarget;
+
+-- Subqueries
+BEGIN;
+MERGE INTO sq_target t
+USING v
+ON tid = sid
+WHEN MATCHED THEN
+    UPDATE SET balance = (SELECT count(*) FROM sq_target)
+;
+SELECT * FROM sq_target WHERE tid = 1;
+ROLLBACK;
+
+BEGIN;
+MERGE INTO sq_target t
+USING v
+ON tid = sid
+WHEN MATCHED AND (SELECT count(*) > 0 FROM sq_target) THEN
+    UPDATE SET balance = 42
+;
+SELECT * FROM sq_target WHERE tid = 1;
+ROLLBACK;
+
+BEGIN;
+MERGE INTO sq_target t
+USING v
+ON tid = sid AND (SELECT count(*) > 0 FROM sq_target)
+WHEN MATCHED THEN
+    UPDATE SET balance = 42
+;
+SELECT * FROM sq_target WHERE tid = 1;
+ROLLBACK;
+
+DROP TABLE sq_target, sq_source CASCADE;
+
+CREATE TABLE pa_target (tid integer, balance float, val text)
+	PARTITION BY LIST (tid);
+
+CREATE TABLE part1 PARTITION OF pa_target FOR VALUES IN (1,4);
+CREATE TABLE part2 PARTITION OF pa_target FOR VALUES IN (2,5,6);
+CREATE TABLE part3 PARTITION OF pa_target FOR VALUES IN (3,8,9);
+CREATE TABLE part4 PARTITION OF pa_target DEFAULT;
+
+CREATE TABLE pa_source (sid integer, delta float);
+-- insert many rows to the source table
+INSERT INTO pa_source SELECT id, id * 10  FROM generate_series(1,14) AS id;
+-- insert a few rows in the target table (odd numbered tid)
+INSERT INTO pa_target SELECT id, id * 100, 'initial' FROM generate_series(1,14,2) AS id;
+
+-- try simple MERGE
+BEGIN;
+MERGE INTO pa_target t
+  USING pa_source s
+  ON t.tid = s.sid
+  WHEN MATCHED THEN
+    UPDATE SET balance = balance + delta, val = val || ' updated by merge'
+  WHEN NOT MATCHED THEN
+    INSERT VALUES (sid, delta, 'inserted by merge');
+SELECT * FROM pa_target ORDER BY tid;
+ROLLBACK;
+
+-- same with a constant qual
+BEGIN;
+MERGE INTO pa_target t
+  USING pa_source s
+  ON t.tid = s.sid AND tid = 1
+  WHEN MATCHED THEN
+    UPDATE SET balance = balance + delta, val = val || ' updated by merge'
+  WHEN NOT MATCHED THEN
+    INSERT VALUES (sid, delta, 'inserted by merge');
+SELECT * FROM pa_target ORDER BY tid;
+ROLLBACK;
+
+-- try updating the partition key column
+BEGIN;
+MERGE INTO pa_target t
+  USING pa_source s
+  ON t.tid = s.sid
+  WHEN MATCHED THEN
+    UPDATE SET tid = tid + 1, balance = balance + delta, val = val || ' updated by merge'
+  WHEN NOT MATCHED THEN
+    INSERT VALUES (sid, delta, 'inserted by merge');
+SELECT * FROM pa_target ORDER BY tid;
+ROLLBACK;
+
+DROP TABLE pa_target CASCADE;
+
+-- The target table is partitioned in the same way, but this time by attaching
+-- partitions which have columns in different order, dropped columns etc.
+CREATE TABLE pa_target (tid integer, balance float, val text)
+	PARTITION BY LIST (tid);
+CREATE TABLE part1 (tid integer, balance float, val text);
+CREATE TABLE part2 (balance float, tid integer, val text);
+CREATE TABLE part3 (tid integer, balance float, val text);
+CREATE TABLE part4 (extraid text, tid integer, balance float, val text);
+ALTER TABLE part4 DROP COLUMN extraid;
+
+ALTER TABLE pa_target ATTACH PARTITION part1 FOR VALUES IN (1,4);
+ALTER TABLE pa_target ATTACH PARTITION part2 FOR VALUES IN (2,5,6);
+ALTER TABLE pa_target ATTACH PARTITION part3 FOR VALUES IN (3,8,9);
+ALTER TABLE pa_target ATTACH PARTITION part4 DEFAULT;
+
+-- insert a few rows in the target table (odd numbered tid)
+INSERT INTO pa_target SELECT id, id * 100, 'initial' FROM generate_series(1,14,2) AS id;
+
+-- try simple MERGE
+BEGIN;
+MERGE INTO pa_target t
+  USING pa_source s
+  ON t.tid = s.sid
+  WHEN MATCHED THEN
+    UPDATE SET balance = balance + delta, val = val || ' updated by merge'
+  WHEN NOT MATCHED THEN
+    INSERT VALUES (sid, delta, 'inserted by merge');
+SELECT * FROM pa_target ORDER BY tid;
+ROLLBACK;
+
+-- same with a constant qual
+BEGIN;
+MERGE INTO pa_target t
+  USING pa_source s
+  ON t.tid = s.sid AND tid = 1
+  WHEN MATCHED THEN
+    UPDATE SET balance = balance + delta, val = val || ' updated by merge'
+  WHEN NOT MATCHED THEN
+    INSERT VALUES (sid, delta, 'inserted by merge');
+SELECT * FROM pa_target ORDER BY tid;
+ROLLBACK;
+
+-- try updating the partition key column
+BEGIN;
+MERGE INTO pa_target t
+  USING pa_source s
+  ON t.tid = s.sid
+  WHEN MATCHED THEN
+    UPDATE SET tid = tid + 1, balance = balance + delta, val = val || ' updated by merge'
+  WHEN NOT MATCHED THEN
+    INSERT VALUES (sid, delta, 'inserted by merge');
+SELECT * FROM pa_target ORDER BY tid;
+ROLLBACK;
+
+DROP TABLE pa_source;
+DROP TABLE pa_target CASCADE;
+
+-- Sub-partitionin
+CREATE TABLE pa_target (logts timestamp, tid integer, balance float, val text)
+	PARTITION BY RANGE (logts);
+
+CREATE TABLE part_m01 PARTITION OF pa_target
+	FOR VALUES FROM ('2017-01-01') TO ('2017-02-01')
+	PARTITION BY LIST (tid);
+CREATE TABLE part_m01_odd PARTITION OF part_m01
+	FOR VALUES IN (1,3,5,7,9);
+CREATE TABLE part_m01_even PARTITION OF part_m01
+	FOR VALUES IN (2,4,6,8);
+CREATE TABLE part_m02 PARTITION OF pa_target
+	FOR VALUES FROM ('2017-02-01') TO ('2017-03-01')
+	PARTITION BY LIST (tid);
+CREATE TABLE part_m02_odd PARTITION OF part_m02
+	FOR VALUES IN (1,3,5,7,9);
+CREATE TABLE part_m02_even PARTITION OF part_m02
+	FOR VALUES IN (2,4,6,8);
+
+CREATE TABLE pa_source (sid integer, delta float);
+-- insert many rows to the source table
+INSERT INTO pa_source SELECT id, id * 10  FROM generate_series(1,14) AS id;
+-- insert a few rows in the target table (odd numbered tid)
+INSERT INTO pa_target SELECT '2017-01-31', id, id * 100, 'initial' FROM generate_series(1,9,3) AS id;
+INSERT INTO pa_target SELECT '2017-02-28', id, id * 100, 'initial' FROM generate_series(2,9,3) AS id;
+
+-- try simple MERGE
+BEGIN;
+MERGE INTO pa_target t
+  USING (SELECT '2017-01-15' AS slogts, * FROM pa_source WHERE sid < 10) s
+  ON t.tid = s.sid
+  WHEN MATCHED THEN
+    UPDATE SET balance = balance + delta, val = val || ' updated by merge'
+  WHEN NOT MATCHED THEN
+    INSERT VALUES (slogts::timestamp, sid, delta, 'inserted by merge');
+SELECT * FROM pa_target ORDER BY tid;
+ROLLBACK;
+
+DROP TABLE pa_source;
+DROP TABLE pa_target CASCADE;
+
+-- some complex joins on the source side
+
+CREATE TABLE cj_target (tid integer, balance float, val text);
+CREATE TABLE cj_source1 (sid1 integer, scat integer, delta integer);
+CREATE TABLE cj_source2 (sid2 integer, sval text);
+INSERT INTO cj_source1 VALUES (1, 10, 100);
+INSERT INTO cj_source1 VALUES (1, 20, 200);
+INSERT INTO cj_source1 VALUES (2, 20, 300);
+INSERT INTO cj_source1 VALUES (3, 10, 400);
+INSERT INTO cj_source2 VALUES (1, 'initial source2');
+INSERT INTO cj_source2 VALUES (2, 'initial source2');
+INSERT INTO cj_source2 VALUES (3, 'initial source2');
+
+-- source relation is an unalised join
+MERGE INTO cj_target t
+USING cj_source1 s1
+	INNER JOIN cj_source2 s2 ON sid1 = sid2
+ON t.tid = sid1
+WHEN NOT MATCHED THEN
+	INSERT VALUES (sid1, delta, sval);
+
+-- try accessing columns from either side of the source join
+MERGE INTO cj_target t
+USING cj_source2 s2
+	INNER JOIN cj_source1 s1 ON sid1 = sid2 AND scat = 20
+ON t.tid = sid1
+WHEN NOT MATCHED THEN
+	INSERT VALUES (sid2, delta, sval)
+WHEN MATCHED THEN
+	DELETE;
+
+-- some simple expressions in INSERT targetlist
+MERGE INTO cj_target t
+USING cj_source2 s2
+	INNER JOIN cj_source1 s1 ON sid1 = sid2
+ON t.tid = sid1
+WHEN NOT MATCHED THEN
+	INSERT VALUES (sid2, delta + scat, sval)
+WHEN MATCHED THEN
+	UPDATE SET val = val || ' updated by merge';
+
+MERGE INTO cj_target t
+USING cj_source2 s2
+	INNER JOIN cj_source1 s1 ON sid1 = sid2 AND scat = 20
+ON t.tid = sid1
+WHEN MATCHED THEN
+	UPDATE SET val = val || ' ' || delta::text;
+
+SELECT * FROM cj_target;
+
+ALTER TABLE cj_source1 RENAME COLUMN sid1 TO sid;
+ALTER TABLE cj_source2 RENAME COLUMN sid2 TO sid;
+
+TRUNCATE cj_target;
+
+MERGE INTO cj_target t
+USING cj_source1 s1
+	INNER JOIN cj_source2 s2 ON s1.sid = s2.sid
+ON t.tid = s1.sid
+WHEN NOT MATCHED THEN
+	INSERT VALUES (s2.sid, delta, sval);
+
+DROP TABLE cj_source2, cj_source1, cj_target;
+
+-- Function scans
+CREATE TABLE fs_target (a int, b int, c text);
+MERGE INTO fs_target t
+USING generate_series(1,100,1) AS id
+ON t.a = id
+WHEN MATCHED THEN
+	UPDATE SET b = b + id
+WHEN NOT MATCHED THEN
+	INSERT VALUES (id, -1);
+
+MERGE INTO fs_target t
+USING generate_series(1,100,2) AS id
+ON t.a = id
+WHEN MATCHED THEN
+	UPDATE SET b = b + id, c = 'updated '|| id.*::text
+WHEN NOT MATCHED THEN
+	INSERT VALUES (id, -1, 'inserted ' || id.*::text);
+
+SELECT count(*) FROM fs_target;
+DROP TABLE fs_target;
+
+-- SERIALIZABLE test
+-- handled in isolation tests
+
+-- prepare
+
+RESET SESSION AUTHORIZATION;
+DROP TABLE target, target2;
+DROP TABLE source, source2;
+DROP FUNCTION merge_trigfunc();
+DROP USER merge_privs;
+DROP USER merge_no_privs;
diff --git a/src/test/regress/sql/privileges.sql b/src/test/regress/sql/privileges.sql
index ac2c3df3a2..214d92257d 100644
--- a/src/test/regress/sql/privileges.sql
+++ b/src/test/regress/sql/privileges.sql
@@ -349,6 +349,114 @@ UPDATE atest5 SET one = 1; -- fail
 SELECT atest6 FROM atest6; -- ok
 COPY atest6 TO stdout; -- ok
 
+-- test column privileges with MERGE
+SET SESSION AUTHORIZATION regress_priv_user1;
+CREATE TABLE mtarget (a int, b text);
+CREATE TABLE msource (a int, b text);
+INSERT INTO mtarget VALUES (1, 'init1'), (2, 'init2');
+INSERT INTO msource VALUES (1, 'source1'), (2, 'source2'), (3, 'source3');
+
+GRANT SELECT (a) ON msource TO regress_priv_user4;
+GRANT SELECT (a) ON mtarget TO regress_priv_user4;
+GRANT INSERT (a,b) ON mtarget TO regress_priv_user4;
+GRANT UPDATE (b) ON mtarget TO regress_priv_user4;
+
+SET SESSION AUTHORIZATION regress_priv_user4;
+
+--
+-- test source privileges
+--
+
+-- fail (no SELECT priv on s.b)
+MERGE INTO mtarget t USING msource s ON t.a = s.a
+WHEN MATCHED THEN
+	UPDATE SET b = s.b
+WHEN NOT MATCHED THEN
+	INSERT VALUES (a, NULL);
+
+-- fail (s.b used in the INSERTed values)
+MERGE INTO mtarget t USING msource s ON t.a = s.a
+WHEN MATCHED THEN
+	UPDATE SET b = 'x'
+WHEN NOT MATCHED THEN
+	INSERT VALUES (a, b);
+
+-- fail (s.b used in the WHEN quals)
+MERGE INTO mtarget t USING msource s ON t.a = s.a
+WHEN MATCHED AND s.b = 'x' THEN
+	UPDATE SET b = 'x'
+WHEN NOT MATCHED THEN
+	INSERT VALUES (a, NULL);
+
+-- this should be ok since only s.a is accessed
+BEGIN;
+MERGE INTO mtarget t USING msource s ON t.a = s.a
+WHEN MATCHED THEN
+	UPDATE SET b = 'ok'
+WHEN NOT MATCHED THEN
+	INSERT VALUES (a, NULL);
+ROLLBACK;
+
+SET SESSION AUTHORIZATION regress_priv_user1;
+GRANT SELECT (b) ON msource TO regress_priv_user4;
+SET SESSION AUTHORIZATION regress_priv_user4;
+
+-- should now be ok
+BEGIN;
+MERGE INTO mtarget t USING msource s ON t.a = s.a
+WHEN MATCHED THEN
+	UPDATE SET b = s.b
+WHEN NOT MATCHED THEN
+	INSERT VALUES (a, b);
+ROLLBACK;
+
+--
+-- test target privileges
+--
+
+-- fail (no SELECT priv on t.b)
+MERGE INTO mtarget t USING msource s ON t.a = s.a
+WHEN MATCHED THEN
+	UPDATE SET b = t.b
+WHEN NOT MATCHED THEN
+	INSERT VALUES (a, NULL);
+
+-- fail (no UPDATE on t.a)
+MERGE INTO mtarget t USING msource s ON t.a = s.a
+WHEN MATCHED THEN
+	UPDATE SET b = s.b, a = t.a + 1
+WHEN NOT MATCHED THEN
+	INSERT VALUES (a, b);
+
+-- fail (no SELECT on t.b)
+MERGE INTO mtarget t USING msource s ON t.a = s.a
+WHEN MATCHED AND t.b IS NOT NULL THEN
+	UPDATE SET b = s.b
+WHEN NOT MATCHED THEN
+	INSERT VALUES (a, b);
+
+-- ok
+BEGIN;
+MERGE INTO mtarget t USING msource s ON t.a = s.a
+WHEN MATCHED THEN
+	UPDATE SET b = s.b;
+ROLLBACK;
+
+-- fail (no DELETE)
+MERGE INTO mtarget t USING msource s ON t.a = s.a
+WHEN MATCHED AND t.b IS NOT NULL THEN
+	DELETE;
+
+-- grant delete privileges
+SET SESSION AUTHORIZATION regress_priv_user1;
+GRANT DELETE ON mtarget TO regress_priv_user4;
+-- should be ok now
+BEGIN;
+MERGE INTO mtarget t USING msource s ON t.a = s.a
+WHEN MATCHED AND t.b IS NOT NULL THEN
+	DELETE;
+ROLLBACK;
+
 -- check error reporting with column privs
 SET SESSION AUTHORIZATION regress_priv_user1;
 CREATE TABLE t1 (c1 int, c2 int, c3 int check (c3 < 5), primary key (c1, c2));
diff --git a/src/test/regress/sql/rowsecurity.sql b/src/test/regress/sql/rowsecurity.sql
index 38e9b38bc4..ed07b45830 100644
--- a/src/test/regress/sql/rowsecurity.sql
+++ b/src/test/regress/sql/rowsecurity.sql
@@ -812,6 +812,162 @@ INSERT INTO document VALUES (4, (SELECT cid from category WHERE cname = 'novel')
 INSERT INTO document VALUES (1, (SELECT cid from category WHERE cname = 'novel'), 1, 'regress_rls_bob', 'my first novel')
     ON CONFLICT (did) DO UPDATE SET dauthor = 'regress_rls_carol';
 
+--
+-- MERGE
+--
+RESET SESSION AUTHORIZATION;
+DROP POLICY p3_with_all ON document;
+
+ALTER TABLE document ADD COLUMN dnotes text DEFAULT '';
+-- all documents are readable
+CREATE POLICY p1 ON document FOR SELECT USING (true);
+-- one may insert documents only authored by them
+CREATE POLICY p2 ON document FOR INSERT WITH CHECK (dauthor = current_user);
+-- one may only update documents in 'novel' category
+CREATE POLICY p3 ON document FOR UPDATE
+  USING (cid = (SELECT cid from category WHERE cname = 'novel'))
+  WITH CHECK (dauthor = current_user);
+-- one may only delete documents in 'manga' category
+CREATE POLICY p4 ON document FOR DELETE
+  USING (cid = (SELECT cid from category WHERE cname = 'manga'));
+
+SELECT * FROM document;
+
+SET SESSION AUTHORIZATION regress_rls_bob;
+
+-- Fails, since update violates WITH CHECK qual on dauthor
+MERGE INTO document d
+USING (SELECT 1 as sdid) s
+ON did = s.sdid
+WHEN MATCHED THEN
+	UPDATE SET dnotes = dnotes || ' notes added by merge1 ', dauthor = 'regress_rls_alice';
+
+-- Should be OK since USING and WITH CHECK quals pass
+MERGE INTO document d
+USING (SELECT 1 as sdid) s
+ON did = s.sdid
+WHEN MATCHED THEN
+	UPDATE SET dnotes = dnotes || ' notes added by merge2 ';
+
+-- Even when dauthor is updated explicitly, but to the existing value
+MERGE INTO document d
+USING (SELECT 1 as sdid) s
+ON did = s.sdid
+WHEN MATCHED THEN
+	UPDATE SET dnotes = dnotes || ' notes added by merge3 ', dauthor = 'regress_rls_bob';
+
+-- There is a MATCH for did = 3, but UPDATE's USING qual does not allow
+-- updating an item in category 'science fiction'
+MERGE INTO document d
+USING (SELECT 3 as sdid) s
+ON did = s.sdid
+WHEN MATCHED THEN
+	UPDATE SET dnotes = dnotes || ' notes added by merge ';
+
+-- The same thing with DELETE action, but fails again because no permissions
+-- to delete items in 'science fiction' category that did 3 belongs to.
+MERGE INTO document d
+USING (SELECT 3 as sdid) s
+ON did = s.sdid
+WHEN MATCHED THEN
+	DELETE;
+
+-- Document with did 4 belongs to 'manga' category which is allowed for
+-- deletion. But this fails because the UPDATE action is matched first and
+-- UPDATE policy does not allow updation in the category.
+MERGE INTO document d
+USING (SELECT 4 as sdid) s
+ON did = s.sdid
+WHEN MATCHED AND dnotes = '' THEN
+	UPDATE SET dnotes = dnotes || ' notes added by merge '
+WHEN MATCHED THEN
+	DELETE;
+
+-- UPDATE action is not matched this time because of the WHEN AND qual.
+-- DELETE still fails because role regress_rls_bob does not have SELECT
+-- privileges on 'manga' category row in the category table.
+MERGE INTO document d
+USING (SELECT 4 as sdid) s
+ON did = s.sdid
+WHEN MATCHED AND dnotes <> '' THEN
+	UPDATE SET dnotes = dnotes || ' notes added by merge '
+WHEN MATCHED THEN
+	DELETE;
+
+SELECT * FROM document WHERE did = 4;
+
+-- Switch to regress_rls_carol role and try the DELETE again. It should succeed
+-- this time
+RESET SESSION AUTHORIZATION;
+SET SESSION AUTHORIZATION regress_rls_carol;
+
+MERGE INTO document d
+USING (SELECT 4 as sdid) s
+ON did = s.sdid
+WHEN MATCHED AND dnotes <> '' THEN
+	UPDATE SET dnotes = dnotes || ' notes added by merge '
+WHEN MATCHED THEN
+	DELETE;
+
+-- Switch back to regress_rls_bob role
+RESET SESSION AUTHORIZATION;
+SET SESSION AUTHORIZATION regress_rls_bob;
+
+-- Try INSERT action. This fails because we are trying to insert
+-- dauthor = regress_rls_dave and INSERT's WITH CHECK does not allow
+-- that
+MERGE INTO document d
+USING (SELECT 12 as sdid) s
+ON did = s.sdid
+WHEN MATCHED THEN
+	DELETE
+WHEN NOT MATCHED THEN
+	INSERT VALUES (12, 11, 1, 'regress_rls_dave', 'another novel');
+
+-- This should be fine
+MERGE INTO document d
+USING (SELECT 12 as sdid) s
+ON did = s.sdid
+WHEN MATCHED THEN
+	DELETE
+WHEN NOT MATCHED THEN
+	INSERT VALUES (12, 11, 1, 'regress_rls_bob', 'another novel');
+
+-- ok
+MERGE INTO document d
+USING (SELECT 1 as sdid) s
+ON did = s.sdid
+WHEN MATCHED THEN
+	UPDATE SET dnotes = dnotes || ' notes added by merge4 '
+WHEN NOT MATCHED THEN
+	INSERT VALUES (12, 11, 1, 'regress_rls_bob', 'another novel');
+
+-- drop and create a new SELECT policy which prevents us from reading
+-- any document except with category 'magna'
+RESET SESSION AUTHORIZATION;
+DROP POLICY p1 ON document;
+CREATE POLICY p1 ON document FOR SELECT
+  USING (cid = (SELECT cid from category WHERE cname = 'manga'));
+
+SET SESSION AUTHORIZATION regress_rls_bob;
+
+-- MERGE can no longer see the matching row and hence attempts the
+-- NOT MATCHED action, which results in unique key violation
+MERGE INTO document d
+USING (SELECT 1 as sdid) s
+ON did = s.sdid
+WHEN MATCHED THEN
+	UPDATE SET dnotes = dnotes || ' notes added by merge5 '
+WHEN NOT MATCHED THEN
+	INSERT VALUES (12, 11, 1, 'regress_rls_bob', 'another novel');
+
+RESET SESSION AUTHORIZATION;
+-- drop the restrictive SELECT policy so that we can look at the
+-- final state of the table
+DROP POLICY p1 ON document;
+-- Just check everything went per plan
+SELECT * FROM document;
+
 --
 -- ROLE/GROUP
 --
diff --git a/src/test/regress/sql/rules.sql b/src/test/regress/sql/rules.sql
index f4ee30ec8f..550b03a4da 100644
--- a/src/test/regress/sql/rules.sql
+++ b/src/test/regress/sql/rules.sql
@@ -1191,6 +1191,39 @@ CREATE RULE rules_parted_table_insert AS ON INSERT to rules_parted_table
 ALTER RULE rules_parted_table_insert ON rules_parted_table RENAME TO rules_parted_table_insert_redirect;
 DROP TABLE rules_parted_table;
 
+--
+-- test MERGE
+--
+CREATE TABLE rule_merge1 (a int, b text);
+CREATE TABLE rule_merge2 (a int, b text);
+CREATE RULE rule1 AS ON INSERT TO rule_merge1
+	DO INSTEAD INSERT INTO rule_merge2 VALUES (NEW.*);
+CREATE RULE rule2 AS ON UPDATE TO rule_merge1
+	DO INSTEAD UPDATE rule_merge2 SET a = NEW.a, b = NEW.b
+	WHERE a = OLD.a;
+CREATE RULE rule3 AS ON DELETE TO rule_merge1
+	DO INSTEAD DELETE FROM rule_merge2 WHERE a = OLD.a;
+
+-- MERGE not supported for table with rules
+MERGE INTO rule_merge1 t USING (SELECT 1 AS a) s
+	ON t.a = s.a
+	WHEN MATCHED AND t.a < 2 THEN
+		UPDATE SET b = b || ' updated by merge'
+	WHEN MATCHED AND t.a > 2 THEN
+		DELETE
+	WHEN NOT MATCHED THEN
+		INSERT VALUES (s.a, '');
+
+-- should be ok with the other table though
+MERGE INTO rule_merge2 t USING (SELECT 1 AS a) s
+	ON t.a = s.a
+	WHEN MATCHED AND t.a < 2 THEN
+		UPDATE SET b = b || ' updated by merge'
+	WHEN MATCHED AND t.a > 2 THEN
+		DELETE
+	WHEN NOT MATCHED THEN
+		INSERT VALUES (s.a, '');
+
 --
 -- Test enabling/disabling
 --
diff --git a/src/test/regress/sql/triggers.sql b/src/test/regress/sql/triggers.sql
index 5336185ed2..c1095e9ce7 100644
--- a/src/test/regress/sql/triggers.sql
+++ b/src/test/regress/sql/triggers.sql
@@ -2114,6 +2114,53 @@ delete from self_ref where a = 1;
 
 drop table self_ref;
 
+--
+-- test transition tables with MERGE
+--
+create table merge_target_table (a int primary key, b text);
+create trigger merge_target_table_insert_trig
+  after insert on merge_target_table referencing new table as new_table
+  for each statement execute procedure dump_insert();
+create trigger merge_target_table_update_trig
+  after update on merge_target_table referencing old table as old_table new table as new_table
+  for each statement execute procedure dump_update();
+create trigger merge_target_table_delete_trig
+  after delete on merge_target_table referencing old table as old_table
+  for each statement execute procedure dump_delete();
+
+create table merge_source_table (a int, b text);
+insert into merge_source_table
+  values (1, 'initial1'), (2, 'initial2'),
+		 (3, 'initial3'), (4, 'initial4');
+
+merge into merge_target_table t
+using merge_source_table s
+on t.a = s.a
+when not matched then
+  insert values (a, b);
+
+merge into merge_target_table t
+using merge_source_table s
+on t.a = s.a
+when matched and s.a <= 2 then
+	update set b = t.b || ' updated by merge'
+when matched and s.a > 2 then
+	delete
+when not matched then
+  insert values (a, b);
+
+merge into merge_target_table t
+using merge_source_table s
+on t.a = s.a
+when matched and s.a <= 2 then
+	update set b = t.b || ' updated again by merge'
+when matched and s.a > 2 then
+	delete
+when not matched then
+  insert values (a, b);
+
+drop table merge_source_table, merge_target_table;
+
 -- cleanup
 drop function dump_insert();
 drop function dump_update();
diff --git a/src/test/regress/sql/with.sql b/src/test/regress/sql/with.sql
index f85645efde..c6b197c327 100644
--- a/src/test/regress/sql/with.sql
+++ b/src/test/regress/sql/with.sql
@@ -862,6 +862,62 @@ RETURNING k, v;
 
 DROP TABLE withz;
 
+-- WITH referenced by MERGE statement
+CREATE TABLE m AS SELECT i AS k, (i || ' v')::text v FROM generate_series(1, 16, 3) i;
+ALTER TABLE m ADD UNIQUE (k);
+
+WITH RECURSIVE cte_basic AS (SELECT 1 a, 'cte_basic val' b)
+MERGE INTO m USING (select 0 k, 'merge source SubPlan' v) o ON m.k=o.k
+WHEN MATCHED THEN UPDATE SET v = (SELECT b || ' merge update' FROM cte_basic WHERE cte_basic.a = m.k LIMIT 1)
+WHEN NOT MATCHED THEN INSERT VALUES(o.k, o.v);
+
+-- Basic:
+WITH cte_basic AS (SELECT 1 a, 'cte_basic val' b)
+MERGE INTO m USING (select 0 k, 'merge source SubPlan' v) o ON m.k=o.k
+WHEN MATCHED THEN UPDATE SET v = (SELECT b || ' merge update' FROM cte_basic WHERE cte_basic.a = m.k LIMIT 1)
+WHEN NOT MATCHED THEN INSERT VALUES(o.k, o.v);
+-- Examine
+SELECT * FROM m where k = 0;
+
+-- See EXPLAIN output for same query:
+EXPLAIN (VERBOSE, COSTS OFF)
+WITH cte_basic AS (SELECT 1 a, 'cte_basic val' b)
+MERGE INTO m USING (select 0 k, 'merge source SubPlan' v) o ON m.k=o.k
+WHEN MATCHED THEN UPDATE SET v = (SELECT b || ' merge update' FROM cte_basic WHERE cte_basic.a = m.k LIMIT 1)
+WHEN NOT MATCHED THEN INSERT VALUES(o.k, o.v);
+
+-- InitPlan
+WITH cte_init AS (SELECT 1 a, 'cte_init val' b)
+MERGE INTO m USING (select 1 k, 'merge source InitPlan' v) o ON m.k=o.k
+WHEN MATCHED THEN UPDATE SET v = (SELECT b || ' merge update' FROM cte_init WHERE a = 1 LIMIT 1)
+WHEN NOT MATCHED THEN INSERT VALUES(o.k, o.v);
+-- Examine
+SELECT * FROM m where k = 1;
+
+-- See EXPLAIN output for same query:
+EXPLAIN (VERBOSE, COSTS OFF)
+WITH cte_init AS (SELECT 1 a, 'cte_init val' b)
+MERGE INTO m USING (select 1 k, 'merge source InitPlan' v) o ON m.k=o.k
+WHEN MATCHED THEN UPDATE SET v = (SELECT b || ' merge update' FROM cte_init WHERE a = 1 LIMIT 1)
+WHEN NOT MATCHED THEN INSERT VALUES(o.k, o.v);
+
+-- MERGE source comes from CTE:
+WITH merge_source_cte AS (SELECT 15 a, 'merge_source_cte val' b)
+MERGE INTO m USING (select * from merge_source_cte) o ON m.k=o.a
+WHEN MATCHED THEN UPDATE SET v = (SELECT b || merge_source_cte.*::text || ' merge update' FROM merge_source_cte WHERE a = 15)
+WHEN NOT MATCHED THEN INSERT VALUES(o.a, o.b || (SELECT merge_source_cte.*::text || ' merge insert' FROM merge_source_cte));
+-- Examine
+SELECT * FROM m where k = 15;
+
+-- See EXPLAIN output for same query:
+EXPLAIN (VERBOSE, COSTS OFF)
+WITH merge_source_cte AS (SELECT 15 a, 'merge_source_cte val' b)
+MERGE INTO m USING (select * from merge_source_cte) o ON m.k=o.a
+WHEN MATCHED THEN UPDATE SET v = (SELECT b || merge_source_cte.*::text || ' merge update' FROM merge_source_cte WHERE a = 15)
+WHEN NOT MATCHED THEN INSERT VALUES(o.a, o.b || (SELECT merge_source_cte.*::text || ' merge insert' FROM merge_source_cte));
+
+DROP TABLE m;
+
 -- check that run to completion happens in proper ordering
 
 TRUNCATE TABLE y;
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index 9fe950b29d..5a83e5f549 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -1267,6 +1267,8 @@ MemoryContextCounters
 MemoryContextData
 MemoryContextMethods
 MemoryStatsPrintFunc
+MergeAction
+MergeActionState
 MergeAppend
 MergeAppendPath
 MergeAppendState
@@ -1274,6 +1276,7 @@ MergeJoin
 MergeJoinClause
 MergeJoinState
 MergePath
+MergeStmt
 MergeScanSelCache
 MetaCommand
 MinMaxAggInfo
-- 
2.14.3 (Apple Git-98)

