Re: prepare in a do loop - Mailing list pgsql-general
| From | Marc Millas |
|---|---|
| Subject | Re: prepare in a do loop |
| Date | |
| Msg-id | CADX_1aZqb8T0heF_ROEiMCn3oM5n8a_up66aZWj8_T7JBV_wYA@mail.gmail.com Whole thread Raw |
| In response to | Re: prepare in a do loop (Tom Lane <tgl@sss.pgh.pa.us>) |
| Responses |
Re: prepare in a do loop
|
| List | pgsql-general |
Hi Tom,
I do read the doc, and understand the caching behaviour of plpgsql.
if in psql I write begin;execute moninsert(randname()); execute moninsert(randname());end;
it does work. And if I put this (begin execute end) inside a do loop it doesnt anymore.
ok the begin execute end is ""pure"" SQL, and the same thing within a do loop is plpgsql
so
postgres=# create function testexec()returns void as $$
postgres$# execute moninsert(randname());
postgres$# end;
postgres$# $$ language plpgsql;
ERREUR: erreur de syntaxe sur ou près de « execute »
LIGNE 2 : execute moninsert(randname());
postgres$# execute moninsert(randname());
postgres$# end;
postgres$# $$ language plpgsql;
ERREUR: erreur de syntaxe sur ou près de « execute »
LIGNE 2 : execute moninsert(randname());
fine, quite coherent.
then
postgres=# create function testexec()returns void as $$
execute moninsert(randname());
end;
$$ language sql;
CREATE FUNCTION
execute moninsert(randname());
end;
$$ language sql;
CREATE FUNCTION
as SQL, legal syntax.. ok
but
postgres=# select testexec();
ERREUR: COMMIT n'est pas autorisé dans une fonction SQL
CONTEXTE : fonction SQL « testexec » lors du lancement
ERREUR: COMMIT n'est pas autorisé dans une fonction SQL
CONTEXTE : fonction SQL « testexec » lors du lancement
a bit more difficult to understand, as such.(where is the commit ??)
so.. the prepare//execute thing can only be used in embedded SQL (as not in any plpg, nor in sql functions.
The doc states :
The SQL standard includes a
PREPARE statement, but it is only for use in embedded SQL. This version of the PREPARE statement also uses a somewhat different syntax.??? where is the difference for the prepare context thing (I dont mean the different syntax part) ??
thanks for clarification
On Mon, Feb 15, 2021 at 5:27 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
Marc Millas <marc.millas@mokadb.com> writes:
> in psql, with a postgres 12.5 db on a centos 7 intel:
> I do create a function named randname() returning a varchar, and a table
> matable with a column prenom varchar(50). then
> postgres=# prepare moninsert(varchar) as
> postgres-# insert into matable(prenoms) values($1);
> PREPARE
> I test it:
> postgres=# execute moninsert(randname());
> INSERT 0 1
> up to now, everything fine. then:
> do $$ begin for counter in 1..1000000 loop execute
> moninsert(randname());end loop;end;$$;
> ERREUR: la fonction moninsert(character varying) n'existe pas
> LIGNE 1 : SELECT moninsert(randname())
> someone can explain ?
EXECUTE in plpgsql has nothing whatever to do with the SQL EXECUTE
command. See the respective documentation.
You don't actually need to use SQL PREPARE/EXECUTE in plpgsql.
If you just write "insert into ..." as a command in a
plpgsql function, it's automatically prepared behind the scenes.
Indeed, one of the common uses for plpgsql's EXECUTE is to stop
a prepared plan from being used when you don't want that ... so
far from being the same thing, they're more nearly opposites.
Perhaps a different name should have been chosen, but we're
stuck now.
regards, tom lane
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