From: Tom Lane <tgl@sss.pgh.pa.us>
To: mischa@ca.sophos.com
Cc: pgsql-performance@postgresql.org
Subject: Re: Bad plan for join to aggregate of join.
Date: Tue, 12 Sep 2006 19:42:30 -0400
Message-ID: <3215.1158104550@sss.pgh.pa.us> (raw)
In-Reply-To: <45071FCC.8090509@ca.sophos.com>
References: <821wqiy0oc.fsf@mid.bfk.de>
<45071FCC.8090509@ca.sophos.com>
Mischa Sandberg <mischa@ca.sophos.com> writes:
> can PG see that a join on an grouped-by field
> can be pushed down into the query as an indexable filter?
No. The GROUP BY serves as a partial optimization fence. If you're
concerned about the speed of this query, I recommend making a different
view in which 'message' is joined inside the GROUP BY.
regards, tom lane
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To: pgsql-performance@postgresql.org
Cc: tgl@sss.pgh.pa.us, mischa@ca.sophos.com
Subject: Re: Bad plan for join to aggregate of join.
In-Reply-To: <3215.1158104550@sss.pgh.pa.us>
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