Unfortunately, at the moment Postgres doesn't support subqueries in
CHECK constraints, so it's seems that you should use trigger to check
what you need, smth like this:
CREATE OR REPLACE FUNCTION foo_check() RETURNS trigger AS $BODY$
BEGIN IF NEW.active = TRUE AND NEW.id IN ( SELECT id FROM foo WHERE active = TRUE AND id = NEW.id ) THEN
RAISE EXCEPTION 'Uniqueness violation on column id (%)', NEW.id; END IF;
RETURN NEW;
END
$BODY$ LANGUAGE plpgsql;
CREATE TRIGGER foo_check BEFORE INSERT OR UPDATE ON foo FOR EACH ROW EXECUTE PROCEDURE foo_check();
On 3/5/06, Jeff Frost <jeff@frostconsultingllc.com> wrote:
> I have a table with the following structure:
>
> Column | Type | Modifiers
> ------------+---------+-----------------------
> active | boolean | not null default true
> id | integer | not null
> (other columns left out)
>
> And would like to make a unique constraint which would only check the
> uniqueness of id if active=true.
>
> So, the following values would be acceptable:
>
> ('f',5)
> ('f',5)
> ('t',5)
>
> But these would not be:
>
> ('t',5)
> ('t',5)
>
> Basically, I want something like:
> ALTER TABLE bar ADD CONSTRAINT foo UNIQUE(active (where active='t'),id)
>
> But the above does not appear to exist. Is there a simple way to create a
> check constraint for this type of situation, or do I need to create a function
> to eval a check constraint?
>
> --
> Jeff Frost, Owner <jeff@frostconsultingllc.com>
> Frost Consulting, LLC http://www.frostconsultingllc.com/
> Phone: 650-780-7908 FAX: 650-649-1954
>
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>
--
Best regards,
Nikolay