From: Greg Stark <gsstark@mit.edu>
To: elein <elein@varlena.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Cc: George Pavlov <gpavlov@mynewplace.com>
Cc: pgsql-sql@postgresql.org
Subject: Re: "large" IN/NOT IN subqueries result in query returning wrong data
Date: 28 Dec 2005 10:47:33 -0500
Message-ID: <878xu55ilm.fsf@stark.xeocode.com> (raw)
In-Reply-To: <20051228003503.GE20674@varlena.com>
References: <CCB89282FCE1024EA3DCE687A96A5164039EBD13@ehost010-6.exch010.intermedia.net>
<3697.1135712691@sss.pgh.pa.us>
<20051228001251.GB20674@varlena.com>
<9416.1135729540@sss.pgh.pa.us>
<20051228003503.GE20674@varlena.com>
elein <elein@varlena.com> writes:
> > Note that the above are not inverses because you changed the lefthand
> > input. You do get consistent results when you just add or omit NOT:
> Yes, you are right. I skipped the permutations to get down to the point.
Remember that NULL means "unknown". So "1 IN (1,2,NULL)" *should* be true
because regardless of what that unknown value is it's still obvious that 1
really is in the list. And "3 NOT IN (1,2,NULL)" is unknown because it depends
on whether that unknown quantity is 3 or not.
IN is the same as "= ANY" so "1 IN (1,2,NULL)" is the same as
"1=1 OR 1=2 OR 1=NULL" which is true even though the last of the three is null.
--
greg
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To: pgsql-sql@postgresql.org
Cc: gsstark@mit.edu, elein@varlena.com, tgl@sss.pgh.pa.us, gpavlov@mynewplace.com
Subject: Re: "large" IN/NOT IN subqueries result in query returning wrong data
In-Reply-To: <878xu55ilm.fsf@stark.xeocode.com>
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