X-Original-To: pgsql-sql-postgresql.org@localhost.postgresql.org
Received: from localhost (unknown [200.46.204.144])
	by svr1.postgresql.org (Postfix) with ESMTP id 02B875E46E3
	for <pgsql-sql-postgresql.org@localhost.postgresql.org>;
	Wed, 18 Aug 2004 15:55:09 -0300 (ADT)
Received: from svr1.postgresql.org ([200.46.204.71])
	by localhost (av.hub.org [200.46.204.144]) (amavisd-new, port 10024)
	with ESMTP id 07792-05
	for <pgsql-sql-postgresql.org@localhost.postgresql.org>;
	Wed, 18 Aug 2004 18:55:12 +0000 (GMT)
Received: from davinci.ethosmedia.com (server226.ethosmedia.com
	[209.128.84.226])
	by svr1.postgresql.org (Postfix) with ESMTP id B0E705E40BA
	for <pgsql-sql@postgresql.org>; Wed, 18 Aug 2004 15:55:03 -0300 (ADT)
Received: from [64.81.245.111] (account josh@agliodbs.com HELO
	temoku.sf.agliodbs.com)
	by davinci.ethosmedia.com (CommuniGate Pro SMTP 4.1.8)
	with ESMTP id 6113477; Wed, 18 Aug 2004 11:56:28 -0700
From: Josh Berkus <josh@agliodbs.com>
Reply-To: josh@agliodbs.com
Organization: Aglio Database Solutions
To: Jan Wieck <JanWieck@Yahoo.com>
Subject: Re: multi column foreign key for implicitly unique columns
Date: Wed, 18 Aug 2004 11:55:34 -0700
User-Agent: KMail/1.6.2
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Richard Huxton <dev@archonet.com>,
	Markus Bertheau <twanger@bluetwanger.de>, olly@lfix.co.uk,
	pgsql-sql@postgresql.org, Bruce Momjian <pgman@candle.pha.pa.us>
References: <1092734724.2627.4.camel@dicaprio.akademie1.de>
	<1803.1092847586@sss.pgh.pa.us> <41239990.1000007@Yahoo.com>
In-Reply-To: <41239990.1000007@Yahoo.com>
MIME-Version: 1.0
Content-Disposition: inline
Content-Type: text/plain;
  charset="iso-8859-1"
Content-Transfer-Encoding: 7bit
Message-Id: <200408181155.34472.josh@agliodbs.com>
X-Virus-Scanned: by amavisd-new at hub.org
X-Spam-Status: No, hits=0.0 tagged_above=0.0 required=5.0 tests=
X-Spam-Level: 
X-Archive-Number: 200408/212
X-Sequence-Number: 18709

Jan,
>
> If a.x is unique, then (b.x, b.y) references (a.x, a.y) is only ensuring
> that the redundant copy of y in b.y stays in sync with a.y.

So?  What's denormalized about that?  His other choice is to use a trigger.

What he's trying to do is ensure that the class selected for the FK 
class_name, field_name relates to the same class_name in objects.

-- 
--Josh

Josh Berkus
Aglio Database Solutions
San Francisco