Thread: temp table existence

Hi all. Is there a way to determine the existence of a TEMP
TABLE? I need to check i it exists before I create it. Doing simple check on pg_class or pg_tables is<br/>not enough
becausethere may be other such tables created in other sessions. Or maybe anyone knows the identification (apart from
'others')of error to trap it with EXCEPTION clause? <br /> 

Hello

On 29/12/2007, Marcin Krawczyk <jankes.mk@gmail.com> wrote:
> Hi all. Is there a way to determine the existence of a TEMP TABLE? I need to
> check i it exists before I create it.
> Doing simple check on pg_class or pg_tables is
> not enough because there may be other such tables created in other sessions.
> Or maybe anyone knows the identification (apart from 'others') of error to
> trap it with EXCEPTION clause?
>

http://www.pgsql.cz/index.php/Automatic_execution_plan_caching_in_PL/pgSQL

Regards
Pavel Stehule

Thanks for the answer but it's not quite sufficient. The code supplied on his page:

CREATE OR REPLACE FUNCTION ...
BEGIN
PERFORM 1 FROM pg_catalog.pg_tables
WHERE tablename = 'xx' AND schemaname LIKE 'pg_temp%';
IF FOUND THEN
TRUNCATE xx;
ELSE
CREATE TEMP TABLE xx(...
END IF;

The function does exactly what I was trying to avoid - simple check the existence of xx table in pg_tables virtualy only by it's name, it's not enough since there may be other temp tables created in seprate sessions. The only thing those temp table differ in pg_tables i schemaname, they have 
that suffix number and in the above mentioned function I would have to be able to retrieve this number somehow.

...
WHERE tablename = 'xx' AND schemaname LIKE 'pg_temp_' || function_to_retieve_suffix() ???
...

That would work. Otherwise all temp tables by the name of xx will be truncated, which I would not like to happen since since they may still be in use.

I just realized something... my bad. It will work since TRUNCATE removes only table from current session.<br /><br
/>Thankyou again.<br />Regards<br /><br /> 

Hello

my solution isn't 100% perfect too. Better is test visibility:

SELECT n.nspname as "Schema", c.relname as "Name", CASE c.relkind WHEN 'r' THEN 'table' WHEN 'v' THEN 'view' WHEN 'i'
THEN 'index' WHEN 'S' THEN 'sequence' WHEN 's' THEN 'special' END as
"Type", r.rolname as "Owner"
FROM pg_catalog.pg_class c    JOIN pg_catalog.pg_roles r ON r.oid = c.relowner    LEFT JOIN pg_catalog.pg_namespace n
ONn.oid = c.relnamespace
 
WHERE c.relkind IN ('r','') AND n.nspname <> 'pg_catalog' -- replace LIKE 'pg_temp%'; AND n.nspname !~ '^pg_toast' AND
pg_catalog.pg_table_is_visible(c.oid)
ORDER BY 1,2;

for existence test this query can be simplified
Regards
Pavel Stehule


On 29/12/2007, Marcin Krawczyk <jankes.mk@gmail.com> wrote:
> I just realized something... my bad. It will work since TRUNCATE removes
> only table from current session.
>
> Thank you again.
> Regards
>
>

------------- Original message ----------------------
From: "Marcin Krawczyk" <jankes.mk@gmail.com>
> Hi all. Is there a way to determine the existence of a TEMP
> TABLE? I need to check i it exists before I create it. Doing simple
> check on pg_class or pg_tables is
> not enough because there may be other such tables created in other sessions.
> Or maybe anyone knows the identification (apart from 'others') of error to
> trap it with EXCEPTION clause?

select  *  from temp_table limit 1;
Trap error 42P01 Undefined table.

--
Adrian Klaver
aklaver@comcast.net

 -

On Dec 29, 2007, at 3:16 PM, Marcin Krawczyk wrote:

> I just realized something... my bad. It will work since TRUNCATE
> removes only table from current session.

If the table exists and you're going to TRUNCATE it before using it,
you could just use DROP TABLE IF EXISTS and then create it.  I don't
know, that feels cleaner to me than TRUNCATEing a table that might
not be available to the session.

Erik Jones

Software Developer | Emma®
erik@myemma.com
800.595.4401 or 615.292.5888
615.292.0777 (fax)

Emma helps organizations everywhere communicate & market in style.
Visit us online at http://www.myemma.com

Hello

On 30/12/2007, Erik Jones <erik@myemma.com> wrote:
>
> On Dec 29, 2007, at 3:16 PM, Marcin Krawczyk wrote:
>
> > I just realized something... my bad. It will work since TRUNCATE
> > removes only table from current session.
>
> If the table exists and you're going to TRUNCATE it before using it,
> you could just use DROP TABLE IF EXISTS and then create it.  I don't
> know, that feels cleaner to me than TRUNCATEing a table that might
> not be available to the session.
>

if you drop temp table in session, you lost all prepared statements
related to table. before 8.3 it means runtime error, now only less
efectivity.


> Erik Jones
>
> Software Developer | Emma(R)
> erik@myemma.com
> 800.595.4401 or 615.292.5888
> 615.292.0777 (fax)
>
> Emma helps organizations everywhere communicate & market in style.
> Visit us online at http://www.myemma.com
>
>
>