efficiency NOT NULL vs. Check Constraint

What is more efficient having a not null constraint on a field or including a NVL check in a check constraint?

ex: not null constraint on fielda AND

    check constraint (fielda IN ('a','b','c'))

 VS.

    check constraint (nvl(fielda,'X') IN ('a','b','c'))

Thanks, Tim Received on Tue Sep 25 2001 - 08:33:25 CDT