Re: Prepared statements in PGSQL functions

Hi Listers,
I want to use prepared statement in a function. Here is my code:

create or replace function generate_data
( integer, integer )
returns integer
as
$BODY$
declare
p_count alias for $1;
p_max_value_id1 alias for $2;
v_max_value_id1 integer ;
v_id1 int;
v_id2 int;
v_filler varchar(200) := repeat('BIGSTRING', 3);
begin
v_id1:= round( (random()* v_max_value_id1)::bigint,0);
v_id2:= round( (random()* v_max_value_id1)::bigint,0);
prepare mystmt( int, int, varchar) as insert into part values ($1,$2,$3);
execute mystmt(v_id1, v_id2, v_filler );
deallocate mystmt;
end;
$BODY$
language plpgsql ;

Definition of table part is :

CREATE TABLE part (
id1 int not null,
id2 int not null,
filler varchar(200)
);

When I try to call my function I am getting the following errors :
postgres=# select * from gen (10, 10 );
ERROR: function mystmt(integer, integer, character varying) does not exist
HINT: No function matches the given name and argument types. You may need to add explicit type casts.
CONTEXT: SQL statement "SELECT mystmt( $1 , $2 , $3 )"
PL/pgSQL function "gen" line 12 at execute statement

How to solve my problem ? Is it possible at all to call prepared statement inside a function at all?

Regards. MILEN

am 14.06.2006, um 15:12:36 +0200 mailte Milen Kulev folgendes:
> How to solve my problem ? Is it possible at all to call prepared statement inside a function at all?

Yes, i have a example:

create or replace function foo() returns text as $$
declare sql text;
begin
sql := 'prepare bla(int) as select now();';
execute sql;
sql := 'execute bla(1);';
execute sql;
return 'ready';
end
$$ language plpgsql;

test=*# select foo();
foo
-------
ready
(1 row)

You should execute strings in plpgsql, not prepared statements.

HTH, Andreas
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Andreas Kretschmer (Kontakt: siehe Header)
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"Milen Kulev" <makulev(at)gmx(dot)net> writes:
> I want to use prepared statement in a function.

Why? You seem not to be aware that plpgsql implicitly prepares
statements behind the scenes.

> prepare mystmt( int, int, varchar) as insert into part values ($1,$2,$3);
> execute mystmt(v_id1, v_id2, v_filler );
> deallocate mystmt;

If that worked it would be *exactly* the same as just doing

insert into part values (v_id1, v_id2, v_filler);

except for being slower due to re-preparing each time through the
function. So don't waste your time trying to outsmart the language.

regards, tom lane

-----Original Message-----
From: pgsql-sql-owner(at)postgresql(dot)org [mailto:pgsql-sql-owner(at)postgresql(dot)org] On Behalf Of Tom Lane
Sent: Wednesday, June 14, 2006 4:35 PM
To: Milen Kulev
Cc: pgsql-sql(at)postgresql(dot)org
Subject: Re: [SQL] Prepared statements in PGSQL functions

"Milen Kulev" <makulev(at)gmx(dot)net> writes:
>> I want to use prepared statement in a function (your comments below). Wanted
just to test the difference ...

Why? You seem not to be aware that plpgsql implicitly prepares statements behind the scenes.

&&>> I already have a version with "direct" insert ( just as you say a couple of lines below)

> prepare mystmt( int, int, varchar) as insert into part values ($1,$2,$3);
> execute mystmt(v_id1, v_id2, v_filler );
> deallocate mystmt;

If that worked it would be *exactly* the same as just doing

insert into part values (v_id1, v_id2, v_filler);

except for being slower due to re-preparing each time through the function. So don't waste your time trying to outsmart
the language.

>> My idea was to prepare the statment once and execute it in a loop many times (within a procedure/function). Anyway,
obviously there is no performance gain in using prepared statement in functions.
Regards. Milen

regards, tom lane

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