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To: Warren Little <wlittle@securitylending.com>
Cc: pgsql-sql@postgresql.org
Subject: Re: Why do the two queries below return different results? 
In-reply-to: <1058388773.5345.8.camel@localhost.localdomain> 
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Comments: In-reply-to Warren Little <wlittle@securitylending.com>
	message dated "16 Jul 2003 14:52:53 -0600"
Date: Sun, 20 Jul 2003 00:54:26 -0400
Message-ID: <20000.1058676866@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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Warren Little <wlittle@securitylending.com> writes:
> Look at the following two queries.
> ...
> and not exists (select pid from casecombo where casepid = secondpid)
> ...
> and casepid not in (select secondpid from casecombo)

> The second query is broken and I don't understand why.

I'll bet there are some NULL values for secondpid in casecombo.
The behavior of NOT IN with NULLs is fairly unintuitive :-(

			regards, tom lane