To: David Jarvis <thangalin@gmail.com>
cc: Thom Brown <thombrown@gmail.com>, pgsql-performance@postgresql.org
Subject: Re: Optimize date query for large child tables: GiST or GIN? 
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Comments: In-reply-to David Jarvis <thangalin@gmail.com>
	message dated "Thu, 20 May 2010 13:09:05 -0700"
Date: Thu, 20 May 2010 16:18:58 -0400
Message-ID: <8132.1274386738@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>

David Jarvis <thangalin@gmail.com> writes:
> I was hoping to eliminate this part of the query:
>         (cast(extract( YEAR FROM m.taken ) + greatest( -1 *
>           sign(
>             (extract( YEAR FROM m.taken )||'-12-31')::date -
>             (extract( YEAR FROM m.taken )||'-01-01')::date ), 0
>         ) AS text)||'-12-31')::date

> That uses functions to create the dates, which is definitely the problem.

Well, it's not the functions per se that's the problem, it's the lack of
a useful index on the expression.  But as somebody remarked upthread,
that expression doesn't look correct at all.  Doesn't the whole
greatest() subexpression reduce to a constant?

			regards, tom lane