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

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