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Re: Slow update

From: Richard Huxton <dev(at)archonet(dot)com>
To: Hilary Forbes <hforbes(at)dmr(dot)co(dot)uk>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: Slow update
Date: 2005-09-12 10:51:17
Message-ID: 43255DA5.9030602@archonet.com (view raw or flat)
Thread:
Lists: pgsql-performance
Hilary Forbes wrote:
> 
> I need to set the value of a field in table A to a value in table B depending on the existence of the record in table B.  So what I have done is
> 
> UPDATE tableA set a.val1=b.somefield FROM tableA a, tableB b WHERE a.key1=b.key1;

Check the EXPLAIN carefully, are you sure the tableA in "UPDATE" is the 
same as that in your "FROM" clause. If so, why are you SETting a.val1?

If not, you've probably got an unconstrained join.
--
   Richard Huxton
   Archonet Ltd

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