To: Ian Barwick <barwick@gmail.com>
Cc: Stephan Szabo <sszabo@megazone.bigpanda.com>,
	Kenneth Gonsalves <lawgon@thenilgiris.com>, pgsql-sql@postgresql.org
Subject: Re: replacing mysql enum
References: <04121110305520.21547@thenilgiris.com>
	<1d581afe04121104255557ea@mail.gmail.com>
	<20041211074227.J30051@megazone.bigpanda.com>
	<1d581afe041211090628da57e@mail.gmail.com>
In-Reply-To: <1d581afe041211090628da57e@mail.gmail.com>
From: Greg Stark <gsstark@mit.edu>
Organization: The Emacs Conspiracy; member since 1992
Date: 11 Dec 2004 12:25:50 -0500
Message-ID: <87llc44uht.fsf@stark.xeocode.com>
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Ian Barwick <barwick@gmail.com> writes:

> What I still don't quite understand is why IN in a CHECK context is
> handled differently to say: select 1 where 'x' in (null,'a','b','c') ?
> This could be a bit of a gotcha for anyone constructing a constraint
> similar to the original poster's and not realising it has no effect.

well

WHERE foo IN (null, ...)

returns null if foo isn't explicitly in the list (ie, "it may or may not equal
the unknown value in the list"). And I think constraints that return null are
deemed to have succeeded.

-- 
greg