From: Thrasher <thrasher@fibers.upc.es>
To: pgsql-sql@postgresql.org
Subject: Re: Unique constraint over null values
Date: Mon, 30 Sep 2002 19:41:58 +0200
Message-ID: <3D988CE6.5070505@fibers.upc.es> (raw)
References: <3D98884F.9070704@fibers.upc.es>
<200209301033.22795.josh@agliodbs.com>
Hi Josh,
I think I'll follow your advice, as this is the method that I had in my
pocket to use if I had no response. I tried with TRIM and other
functions in the CHECK constraint, but I guess that I cannot use
functions over a check field.
It surprised me, but anyway, I'll do that.
Thanks a lot for your prompt reply
Thrasher
Josh Berkus wrote:
> 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?
>
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Cc: thrasher@fibers.upc.es
Subject: Re: Unique constraint over null values
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