From: Andreas Joseph Krogh <andreak@officenet.no>
Organization: OfficeNet AS
To: pgsql-sql@postgresql.org
Subject: Re: Constraint question
Date: Thu, 18 May 2006 21:05:55 +0200
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On Thursday 18 May 2006 18:38, Markus Schaber wrote:
> Hi, Andreas,
>
> Andreas Joseph Krogh wrote:
> > create table onp_crm_businessfield_company(
> > businessfield_id integer not null references onp_crm_businessfield(id),
> > company_id integer not null references onp_crm_relation(id),
> > is_preferred boolean,
> > UNIQUE(businessfield_id, company_id)
> > );
> >
> > I want a constraint on "is_preffered" so that it's only allowed to be s=
et
> > once pr. businessfield_id pr. company so that only one businessfield can
> > be preferred for a company. Does anyone have an idea how to enforce thi=
s?
>
> CREATE UNIQUE INDEX foo ON onp_crm_businessfield_company(company_id)
> WHERE is_prefferred;

Thanks.
I also figured out that an index like this also works:
UNIQUE(company_id, is_preferred)
This works because NULL =3D NULL is false. But I guess your solution is cle=
aner.

=2D-=20
Andreas Joseph Krogh <andreak@officenet.no>
Senior Software Developer / Manager
gpg public_key: http://dev.officenet.no/~andreak/public_key.asc
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