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Message-ID: <4f4c2a010703270621h5137a4e5rb515a9be9034a543@mail.gmail.com>
Date: Tue, 27 Mar 2007 09:21:44 -0400
From: "Jon Horsman" <horshaq@gmail.com>
To: pgsql-sql@postgresql.org
Subject: Foreign Unique Constraint
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I was wondering if someone could help point me in the right direction
w.r.t. foreign unique constraints.  I'm working on a legacy database
and have a new requirement and am not sure how to do it.

I have something like this

create table table1 (
id SERIAL PRIMARY KEY
extension UNIQUE,
<other fields>
)

create table table2 (
id SERIAL PRIMARY KEY
extension UNIQUE,
<different fields>
)

Basically table 1 and table 2 both have the concept of an extension
that must be unique but the rest of the info in the tables are
different.  I need to ensure that if i add an entry to table 1 with
extension 1000 that it will fail if there is already an entry in
table2 with the same extension.

Essentially i need to do something like the following but i get errors
saying this can't be done.

alter table table1 add check (extension <> table2.extension);

It should be noted i am using pg version 7.4.13 and this can't change.

Thanks for any help you can offer.

Jon.