Thread: RFC: Query Planner making a distinction between Cross Database and Cross Schema ?

Hey there everyone.
Sorry for what seems to be a rather strange
thought but, could we change the seperator used to
distinguish 'cross-database' vs 'cross-schema' ?
For example, i would expect the following
to work:
CREATE OR REPLACE FUNCTION test_autohist() RETURNS triggerAS 'BEGIN           INSERT INTO history.test2 VALUES
(new.field1,history.test_hist.nextval(),new.field2, new.field3, new.field4, new.creation_id, new.creation_date,
new.creation_id,new.creation_date);           RETURN ;           END;' LANGUAGE 'plpgsql';CREATE TRIGGER
test_autohist_trigAFTERINSERT OR UPDATE ON testFOR EACH ROWEXECUTE PROCEDURE test_autohist();
 

However, when i try it, as far as i can tell,
the planner parses it down, finds that the schema isnt
in the current 'search_path' and thus thinks its a cross
database call.
I understand that it may take the planner a 
while to go through all the available schema's to then
deduce that it isnt infact a schema at all and return
the fact that 'cross-database queries are currently not
implemented', therefore, in the realm of crazy idea, 
would it be possible to change the notation to reference
another db ?
I was thinking something along the lines of '@',
but i guess any other non-important ascii character would
make sense.
That way, the planner could decide wether or not
to attempt a schema resolution (history.table1) or database
resolution (live@table4).
Please note, i am not asking for any sort of 
'make cross-database work', merely asking if some sort
of 'clarification' between cross-database and cross-schema
would be beneficial. 
Ideas ? Comments ? 
regardsStef

> Ummmm.  Postgresql doesn't natively support cross database queries...
> 

I know, but it does schema's, and currently, the same
notation is used to specify schema's as 'cross database'.

So the planner often reports 'cross-database not allowed'
in areas where it should at least report 'cross-schema
support is unavailable for this'

case in point, the example trigger. i would have expected
deliberate schemaname.table during an insert to work, but
instead the parser complains about cross-database.

this is why i am saying that if the parser could identify
schema vs database naming, it would help in clarification
of areas where the parser/planner seems to get 'confused'
about what the object is (schema vs database)

currently:  history.table1   <-- schema           history2.table1  <-- database

whereas what i am saying is:           history.table1   <-- schema           history2@table1  <-- database


readability and consistancy is what i am driving at
here, although it would then be possible for the triggers
to be able to insert/update into schema's that are
specifically named instead of coming back with a 
'cross-database not allowed' (when i am trying
to do cross-schema :)


regards
Stef

Ummmm.  Postgresql doesn't natively support cross database queries...

On Thu, 12 Feb 2004, Stef wrote:

> Hey there everyone.
> 
>     Sorry for what seems to be a rather strange
> thought but, could we change the seperator used to
> distinguish 'cross-database' vs 'cross-schema' ?
> 
>     For example, i would expect the following
> to work:
> 
>     CREATE OR REPLACE FUNCTION test_autohist() RETURNS trigger
>     AS 'BEGIN
>             INSERT INTO history.test2 VALUES (new.field1,history.test_hist.nextval(), new.field2, new.field3,
new.field4,new.creation_id, new.creation_date, new.creation_id, new.creation_date);
 
>             RETURN ;
>             END;' LANGUAGE 'plpgsql';
>  
>     CREATE TRIGGER test_autohist_trig
>     AFTER INSERT OR UPDATE ON test
>     FOR EACH ROW
>     EXECUTE PROCEDURE test_autohist();
> 
> 
>     However, when i try it, as far as i can tell,
> the planner parses it down, finds that the schema isnt
> in the current 'search_path' and thus thinks its a cross
> database call.
> 
>     I understand that it may take the planner a 
> while to go through all the available schema's to then
> deduce that it isnt infact a schema at all and return
> the fact that 'cross-database queries are currently not
> implemented', therefore, in the realm of crazy idea, 
> would it be possible to change the notation to reference
> another db ?
> 
>     I was thinking something along the lines of '@',
> but i guess any other non-important ascii character would
> make sense.
> 
>     That way, the planner could decide wether or not
> to attempt a schema resolution (history.table1) or database
> resolution (live@table4).
> 
>     
>     Please note, i am not asking for any sort of 
> 'make cross-database work', merely asking if some sort
> of 'clarification' between cross-database and cross-schema
> would be beneficial. 
> 
>     Ideas ? Comments ? 
> 
>     regards
>     Stef
> 
> ---------------------------(end of broadcast)---------------------------
> TIP 9: the planner will ignore your desire to choose an index scan if your
>       joining column's datatypes do not match
> 

Stef <stef@chronozon.artofdns.com> writes:
>     For example, i would expect the following
> to work:

>     CREATE OR REPLACE FUNCTION test_autohist() RETURNS trigger
>     AS 'BEGIN
>             INSERT INTO history.test2 VALUES (new.field1,history.test_hist.nextval(), new.field2, new.field3,
new.field4,new.creation_id, new.creation_date, new.creation_id, new.creation_date);
 

Why would you expect that to work?

The problem is with this bit:history.test_hist.nextval()
which is a cross-database function reference per the standard SQL syntax
for such things.  (If you were in the history database, it wouldn't be
cross-database, but would refer to the nextval() function in the local
test_hist schema.)

I am not sure what you meant here, but I cannot see any need to
introduce a nonstandard syntax to resolve it.
        regards, tom lane