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From: Olivier Pala <olivier.pala@xgs-france.com>
To: pgsql-performance@postgresql.org
Cc: Olivier Pala <olivier.pala@xgs-france.com>
Subject: UNION and bad performance
Date: Thu, 09 Dec 2010 11:52:14 +0100
Message-ID: <4D00B4DE.3030508@xgs-france.com> (raw)

Hi,

I have a performance trouble with UNION query


First I have this view :

     SELECT a,b,c FROM table1, table2 WHERE jointure AND condition

     Result : 150 000 records in 1~2 s



Then, I adding an UNION into the same view :

     SELECT a,b,c FROM table1, table2 WHERE jointure AND condition
     UNION
     SELECT a,b,c FROM table3

     Result : 150 200 records in 6~7 s


Why, do I have bad performance only for 200 adding records ?

Thanks

*SGBD : Postgres 8.3 et 8.4*

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