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Home -> Community -> Usenet -> comp.databases.theory -> Re: No exceptions?
J M Davitt wrote:
>
> I think I got it. Am I correct in understanding that JH said,
> "If an empty candidate key is declared, any other keys are
> superkeys?"
In fact we can go further: if an empty key exists, then *all* sets of attributes are superkeys.
A superkey is a set of attributes some subset of which is a candidate key.
The empty set is a subset of every set.
Marshall Received on Sat Jul 01 2006 - 13:13:28 CDT
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