From: A. Kretschmer <andreas.kretschmer@schollglas.com>
To: pgsql-sql@postgresql.org
Subject: Re: uniqueness constraint with NULLs
Date: Mon, 29 Jun 2009 08:26:02 +0200
Message-ID: <20090629062602.GB24737@a-kretschmer.de> (raw)
In-Reply-To: <4A485431.3080707@cs.anu.edu.au>
References: <4A485431.3080707@cs.anu.edu.au>
In response to Robert Edwards :
> Can anyone suggest a way that I can impose uniqueness on a and b when
> c is NULL?
Sure, use a functional index:
test=# create table bobtest (a int, b int, c int);
CREATE TABLE
test=*# create unique index idx_bobtest on
bobtest(a,b,coalesce(c::text,'NULL'));
CREATE INDEX
test=*# insert into bobtest (a, b) values (1, 4);
INSERT 0 1
test=*# insert into bobtest (a, b, c) values (1, 4, NULL);
ERROR: duplicate key value violates unique constraint "idx_bobtest"
test=!#
Regards, Andreas
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Andreas Kretschmer
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To: pgsql-sql@postgresql.org
Cc: andreas.kretschmer@schollglas.com
Subject: Re: uniqueness constraint with NULLs
In-Reply-To: <20090629062602.GB24737@a-kretschmer.de>
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