From: Josh Berkus <josh@agliodbs.com>
To: Markus Bertheau <twanger@bluetwanger.de>
To: olly@lfix.co.uk
Cc: pgsql-sql@postgresql.org
Subject: Re: multi column foreign key for implicitly unique columns
Date: Tue, 17 Aug 2004 19:45:15 -0700
Message-ID: <200408171945.15663.josh@agliodbs.com> (raw)
In-Reply-To: <1092736197.2627.12.camel@dicaprio.akademie1.de>
References: <1092734724.2627.4.camel@dicaprio.akademie1.de>
<1092735576.28365.48.camel@linda>
<1092736197.2627.12.camel@dicaprio.akademie1.de>
Markus,
Hey, I see you figured out a workaround to writing a trigger for this. Let's
see if we can make it work.
ERROR: there is no unique constraint matching given keys
for referenced table "objects"
The reason for this is that CASCADE behavior gets quite odd when there is an
FK reference to a non-unique column. We used to allow it, in 7.1, and I was
responsible for a number of bug reports that led to us disallowing it. It
should be theoretically implementable and relationally sound but will require
a *lot* of troubleshooting to make work. So far, nobody's really interested
enough.
However, you have an easy way out:
ALTER TABLE objects ADD CONSTRAINT obj_unq_2 UNIQUE (name, class_name);
This will add the unique constraint that Postgres wants without changing your
data at all.
--
Josh Berkus
Aglio Database Solutions
San Francisco
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To: pgsql-sql@postgresql.org
Cc: josh@agliodbs.com, twanger@bluetwanger.de, olly@lfix.co.uk
Subject: Re: multi column foreign key for implicitly unique columns
In-Reply-To: <200408171945.15663.josh@agliodbs.com>
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