Re: Bad plan when join on function

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
Cc: Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>, zotov(at)oe-it(dot)ru, pgsql-performance(at)postgresql(dot)org
Subject: Re: Bad plan when join on function
Date: 2011-01-17 21:33:44
Message-ID: 21547.1295300024@sss.pgh.pa.us
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Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> writes:
> it should to work without functional index - but not sure about effectivity

As long as the function is VOLATILE, the planner can't use any
intelligent query plan. Merge or hash join both require at least
stable join keys.

regards, tom lane

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