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From: Josh Berkus <josh@agliodbs.com>
Reply-To: josh@agliodbs.com
Organization: Aglio Database Solutions
To: Thrasher <thrasher@fibers.upc.es>
Subject: Re: Unique constraint over null values
Date: Mon, 30 Sep 2002 10:50:05 -0700
References: <3D98884F.9070704@fibers.upc.es>
	<200209301033.22795.josh@agliodbs.com>
	<3D988CE6.5070505@fibers.upc.es>
In-Reply-To: <3D988CE6.5070505@fibers.upc.es>
Cc: pgsql-sql@postgresql.org
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Message-Id: <200209301050.05473.josh@agliodbs.com>


Thrasher,

> I think I'll follow your advice, as this is the method that I had in my=
=20
> pocket to use if I had no response. I tried with TRIM and other=20
> functions in the CHECK constraint, but I guess that I cannot use=20
> functions over a check field.
>=20
> It surprised me, but anyway, I'll do that.
>=20
> Thanks a lot for your prompt reply

No problem.  You should also add a second constraint:=20
CHECK ((type =3D 'x' AND data2 <> 'blank value') OR (type =3D 'y' AND data2=
 =3D=20
'blank value'))

To enforce your other criterion.=20=20

Keeop in mind that depending on the rest of your data structure, there are=
=20
probably 8 different ways to approach this problem.  I'd reccomend, in fact=
,=20
a quick reading of Pascal's "Practical Issues in Database Management" on=20
normalization to see the different table structures that might work for you.

--=20
-Josh Berkus
 Aglio Database Solutions
 San Francisco