From: Josh Berkus <josh@agliodbs.com>
To: Thrasher <thrasher@fibers.upc.es>
To: pgsql-sql@postgresql.org
Subject: Re: Unique constraint over null values
Date: Mon, 30 Sep 2002 10:33:22 -0700
Message-ID: <200209301033.22795.josh@agliodbs.com> (raw)
In-Reply-To: <3D98884F.9070704@fibers.upc.es>
References: <3D98884F.9070704@fibers.upc.es>
Thrasher,
> where type can be 's' for 'single' and 'x' for extended, so s should
> mean that there is only the type and data1 field, and x means that all
> fields are set.
>
> How can I set a unique constraint like CHECK (type = 's' AND UNIQUE
> (type, data1)) OR (type = 'x' AND UNIQUE (type, data1, data2)) ?
>
> The documentation says that 2 NULL values are different, so no unique
> constraint can be set over it.
Simple. Don't use NULLs. NULL means "unknown". You should use a
differnent value, such as a blank string or "N/A" or "000000000000000" to
represent "intentionally left blank".
Then you can set data2 NOT NULL and use a regular UNIQUE constraint.
BTW, you have defined your data columns as CHAR, not VARCHAR. You do know
that this implies that your data columns will be *exactly* 16 characters in
length?
--
-Josh Berkus
Aglio Database Solutions
San Francisco
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To: pgsql-sql@postgresql.org
Cc: josh@agliodbs.com, thrasher@fibers.upc.es
Subject: Re: Unique constraint over null values
In-Reply-To: <200209301033.22795.josh@agliodbs.com>
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