Received: from localhost (maia-1.hub.org [200.46.204.191])
	by postgresql.org (Postfix) with ESMTP id C0BD69FBEF0
	for <pgsql-sql-postgresql.org@postgresql.org>;
	Fri, 16 Mar 2007 13:18:15 -0300 (ADT)
Received: from postgresql.org ([200.46.204.71])
	by localhost (mx1.hub.org [200.46.204.191]) (amavisd-new, port 10024)
	with ESMTP id 16018-06 for <pgsql-sql-postgresql.org@postgresql.org>;
	Fri, 16 Mar 2007 13:18:01 -0300 (ADT)
X-Greylist: from auto-whitelisted by SQLgrey-1.7.4
Received: from sss.pgh.pa.us (sss.pgh.pa.us [66.207.139.130])
	by postgresql.org (Postfix) with ESMTP id B1EEB9FBE7E
	for <pgsql-sql@postgresql.org>; Fri, 16 Mar 2007 13:17:43 -0300 (ADT)
Received: from sss2.sss.pgh.pa.us (tgl@localhost [127.0.0.1])
	by sss.pgh.pa.us (8.13.6/8.13.6) with ESMTP id l2GGHfSC007758;
	Fri, 16 Mar 2007 12:17:41 -0400 (EDT)
To: "Travis Whitton" <tinymountain@gmail.com>
cc: pgsql-sql@postgresql.org
Subject: Re: Grabbing Newest Records From Duplicates 
In-reply-to: <cf9b4f3e0703160855q537eafe6yf3c3bbea090e5b6e@mail.gmail.com> 
References: <cf9b4f3e0703160828s2cc0b9v6c01db6e8634e37e@mail.gmail.com>
	<7240.1174059340@sss.pgh.pa.us>
	<cf9b4f3e0703160855q537eafe6yf3c3bbea090e5b6e@mail.gmail.com>
Comments: In-reply-to "Travis Whitton" <tinymountain@gmail.com>
	message dated "Fri, 16 Mar 2007 10:55:33 -0500"
Date: Fri, 16 Mar 2007 12:17:41 -0400
Message-ID: <7757.1174061861@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
X-Virus-Scanned: Maia Mailguard 1.0.1
X-Archive-Number: 200703/232
X-Sequence-Number: 27870

"Travis Whitton" <tinymountain@gmail.com> writes:
> One last question, using the "weather report" example, is it going to
> improve performance for the DISTINCT ON query to add an index to the
> location and time columns?

A two-column index matching the ORDER BY that you use might help,
or then again might not --- for full-table scans it's often faster
to sort than to try to use an index.

			regards, tom lane