Re: Constraint Problem

On Mon, 3 Nov 2003, Ron St-Pierre wrote:

> Tom Lane wrote:
>
> >Ron St-Pierre <rstpierre@syscor.com> writes:
> >
> >
> >>I just want to constrain the ysnDefault field to only allow one TRUE
> >>value for any companyID/associationID pair, with no restrictions on the
> >>number of FALSES.
> >>
> >>
> >
> >You could do that with a partial unique index.  There is an example
> >at the bottom of
> >http://www.postgresql.org/docs/7.3/static/indexes-partial.html
> >
> >            regards, tom lane
> >
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> >
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> >
> >
> >
> >
> This is not quite what I need. I need to create a constraint to allow
> only -one- of
>     company<->association<->default(=true) value
> but any number of
>     company<->association<->default(=false) values
>
> I've tried many different ALTER TABLE ... CREATE CONSTRAINT variations,
> all without success.

Wouldn't a unique constraint on those three fields do this?  Nulls don't
violate unique constraints.  Does that work, or did I miss too much of
this conversation?