Re: Constraint question

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 set
> > 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 this?
>
> 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 = NULL is false. But I guess your solution is cleaner.

--
Andreas Joseph Krogh <andreak@officenet.no>
Senior Software Developer / Manager
gpg public_key: http://dev.officenet.no/~andreak/public_key.asc
------------------------+---------------------------------------------+
OfficeNet AS            | The most difficult thing in the world is to |
Hoffsveien 17           | know how to do a thing and to watch         |
PO. Box 425 Skøyen      | somebody else doing it wrong, without       |
0213 Oslo               | comment.                                    |
NORWAY                  |                                             |
Phone : +47 22 13 01 00 |                                             |
Direct: +47 22 13 10 03 |                                             |
Mobile: +47 909  56 963 |                                             |
------------------------+---------------------------------------------+