Re: What to call this operator?
Date: 3 Jul 2005 10:10:22 -0700
Message-ID: <1120410621.980966.178660_at_z14g2000cwz.googlegroups.com>
Jan Hidders wrote:
> Marshall Spight wrote:
> > Jan Hidders wrote:
> >>Marshall Spight wrote:
> >>
> >>The rule is that if we take the natural join of R and S then we can
> >>derive a candidate key K for the result if K is a candidate key of both
> >>R and S. Is that what you wanted to hear?
> >
> > That seems correct but incomplete. [...]
> Nope. [...]
D'oh!
> > We also need some kind of fallback rule, such that if we cannot
> > derive any keys for the relation, then the union of all columns
> > is a key.
>
> Indeed. Of course the situation gets much interesting if you also take
> other constraints into account such as functional dependencies.
Are you aware of a comprehensive treatment of this issue? I am quite anxious to learn how it's done, and not the least bit confident in my ability to derive the answers from first principles.
Marshall Received on Sun Jul 03 2005 - 19:10:22 CEST