From: Robert Edwards <bob@cs.anu.edu.au>
To: A. Kretschmer <andreas.kretschmer@schollglas.com>
Cc: pgsql-sql@postgresql.org
Subject: Re: uniqueness constraint with NULLs
Date: Mon, 29 Jun 2009 17:08:34 +1000
Message-ID: <4A486872.5060906@cs.anu.edu.au> (raw)
In-Reply-To: <20090629062602.GB24737@a-kretschmer.de>
References: <4A485431.3080707@cs.anu.edu.au>
<20090629062602.GB24737@a-kretschmer.de>
A. Kretschmer wrote:
> 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
Beautiful!
Many thanks,
Bob Edwards.
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To: pgsql-sql@postgresql.org
Cc: bob@cs.anu.edu.au, andreas.kretschmer@schollglas.com
Subject: Re: uniqueness constraint with NULLs
In-Reply-To: <4A486872.5060906@cs.anu.edu.au>
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