Re: thinking about UPDATE

"Dan" <guntermann_at_verizon.com> wrote in message news:4I3Mc.33048$gt1.2313_at_nwrddc02.gnilink.net...
>
> "Jan Hidders" <jan.hidders_at_REMOVETHIS.pandora.be> wrote in message
> news:pan.2004.07.23.07.26.28.218478_at_REMOVETHIS.pandora.be...
> > On Fri, 23 Jul 2004 01:43:23 +0000, D Guntermann wrote:
> > >
[snip]
>
> I don't know if you have your Date *_Intro to database systems_* book
handy
> (7th Ed), but if you do, perhaps you could check out problem 10.7 on page
> 341 (the answer is on page 344). The question is phrased as, "List all
the
> FDs satisfied by the shipments relvar SP."
>
> To give an indication, part of the answer goes something like this:
>
> {S#} -> {S#}
> {S#} -> {}
>
> {P#} -> { P#}
> {P#} -> {}
>
> { QTY } -> { QTY }
> { QTY } -> {}
>
> {} -> {}
>
> The last is the only time an empty set is on the LHS and is has one and
only
> one result, the empty set.
>
> What do you think?
>

Never mind. In the wee late hours I overlooked the fact that the constraint FD {}->{set of attributes} doesn't hold for relvar SP. OK. Now I'm 99% convinced.

> >
> > -- Jan Hidders
>
> Regards,
>
> - Dan
>
>
Received on Fri Jul 23 2004 - 10:33:51 CEST