Re: Functional Dependencies > Uniqueness Constraints

Marshall wrote:
> Geeze, it's deader than a dotcom startup in here.
>
> Okay, fine. I propose that a good relational DBMS should
> not have any special feature for enforcing uniqueness constraints.
> Instead, it should be able to record and enforce functional
> dependencies.

Obviously a DBMS that can express general FDs can express more than one that can just express CKs, except if you alway normalize to BCNF. But that doesn't mean there shouldn't be a special notion of CK. Determining if a set of fields is a CK on the basis of the known FDs is actually an NP-complete problem, so if the user is so kind to indicate them explicitly that is useful. :-)

• Jan Hidders