Re: Constraint that compares and limits field values

On Wed, Jan 25, 2006 at 08:39:00AM -0800, MargaretGillon@chromalloy.com wrote:
> I have taken your suggestion and changed the values to NULL for the empty
> foreign keys. Thank you for the constraint. I modified it to check for
> NULL and it works great.
>
> ALTER TABLE event
>  ADD CONSTRAINT two_nulls_1 CHECK (((((evenid1 IS NULL) AND (evevid1 IS
> NULL)) OR ((evevid1 IS NULL) AND (evreid1 IS NULL))) OR ((evenid1 IS NULL)
> AND (evreid1 IS NULL))));

Is there a requirement that exactly one column be NOT NULL?  If so
then you'll need to add a check for that because this constraint
would allow all three to be NULL.

--
Michael Fuhr