Message-ID: <4D670B53.70003@agliodbs.com>
Date: Thu, 24 Feb 2011 17:52:19 -0800
From: Josh Berkus <josh@agliodbs.com>
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To: Shaun Thomas <sthomas@peak6.com>
CC: Dave Crooke <dcrooke@gmail.com>,
	Kevin Grittner <Kevin.Grittner@wicourts.gov>,
	Michael Glaesemann <grzm@seespotcode.net>, pgsql-performance@postgresql.org
Subject: Re: Picking out the most recent row using a time stamp
 column
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	<4D66F5B0.5080502@agliodbs.com> <4D66FEB9.6000501@peak6.com>
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> Why did you use row_number instead of rank?

Because I assumed he only wanted one row in the event of ties.

Hmmm, although with that schema, there won't be ties.  So it's pretty
much arbitrary then.

> I am now curious how the speed compares though. I still think the
> DISTINCT ON will be faster, but it would be a great surprise.

Hopefully we'll find out!  The windowing functions are usually much
faster for me.  I think in 9.0 or 9.1 someone replumbed DISTINCT ON to
use a bunch of the window function internals, at which point it'll cease
to matter.

-- 
                                  -- Josh Berkus
                                     PostgreSQL Experts Inc.
                                     http://www.pgexperts.com