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Re: EXISTS optimization

From: Martijn van Oosterhout <kleptog(at)svana(dot)org>
To: Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-hackers(at)postgresql(dot)org,pgsql-performance(at)postgresql(dot)org,Andrea Olson <Aolson(dot)CCAP(dot)Courts(at)wicourts(dot)gov>,Bill Severson <BSEVERS(dot)CCAP(dot)Courts(at)wicourts(dot)gov>,John Hutchins <jhutchi(dot)CCAP(dot)Courts(at)wicourts(dot)gov>,Randy Peterson <RPETERS(dot)CCAP(dot)Courts(at)wicourts(dot)gov>,Shannon Spranger <ssprang(dot)CCAP(dot)Courts(at)wicourts(dot)gov>
Subject: Re: EXISTS optimization
Date: 2007-03-24 13:07:59
Message-ID: 20070324130759.GA1089@svana.org (view raw or flat)
Thread:
Lists: pgsql-hackerspgsql-performance
On Fri, Mar 23, 2007 at 05:30:27PM -0500, Kevin Grittner wrote:
> I don't understand -- TRUE OR UNKNOWN evaluates to TRUE, so why would
> the IN need to continue?  I'm not quite following the rest; could you
> elaborate or give an example?  (Sorry if I'm lagging behind the rest
> of the class here.)

You're right, I'm getting confused with the interaction of NULL and NOT
IN.

The multiple evaluation thing still applies, but that's minor.

Have a nice day,
-- 
Martijn van Oosterhout   <kleptog(at)svana(dot)org>   http://svana.org/kleptog/
> From each according to his ability. To each according to his ability to litigate.

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