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Message-ID: <4B66DD75.5010506@radev.net>
Date: Mon, 01 Feb 2010 15:56:05 +0200
From: "Milen A. Radev" <milen@radev.net>
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CC: pgsql-sql@postgresql.org
Subject: Re: selecting rows tagged with "a" but not "b"
References: <11366-1265031099-334353@sneakemail.com>
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8q5tmkyqry@sneakemail.com написа:
> Hi,
> 
> I have a two tables:
> 
> article
> articleID, name, content
> 
> tags
> articleID, tag
> 
> I want to find all articles that are tagged with "a" but not "b"
> 
> how do I do this?
> 
> what I'd like to do is:
> 
> <wishful thinking>
> select articleID from tags where tag="a"
> SUBTRACT
> select articleID from tags where tab="b"
> </wishful thinking>
> 
> how do I do this in real SQL?

Replace "SUBSTRACT" with "EXCEPT" 
(http://www.postgresql.org/docs/current/static/sql-select.html#SQL-EXCEPT).




-- 
Milen A. Radev