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To: Andrew Perrin <clists@perrin.socsci.unc.edu>
Cc: Stephan Szabo <sszabo@megazone23.bigpanda.com>,
	pgsql-sql@postgresql.org
Subject: Re: LIMIT within UNION? 
In-reply-to: <Pine.LNX.4.21.0209121601370.32000-100000@perrin.socsci.unc.edu> 
References: <Pine.LNX.4.21.0209121601370.32000-100000@perrin.socsci.unc.edu>
Comments: In-reply-to Andrew Perrin <clists@perrin.socsci.unc.edu>
	message dated "Thu, 12 Sep 2002 16:03:54 -0400"
Date: Thu, 12 Sep 2002 16:18:19 -0400
Message-ID: <9596.1031861899@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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Andrew Perrin <clists@perrin.socsci.unc.edu> writes:
> Interesting - this would count on the UNION including all cases in the
> first query before those in the second query. Are UNIONed records
> presented in any predictable order?

If you can use UNION ALL then this would be pretty safe to rely on.
If you must use UNION (to eliminate dups) then it won't work.

			regards, tom lane