Re: Basic question?What 's the key if there 's no FD(Functional Dependencies)?
Date: 7 Nov 2006 10:20:10 -0800
Message-ID: <1162923610.519747.11710_at_k70g2000cwa.googlegroups.com>
paul c wrote:
> Aloha Kakuikanu wrote:
> > NENASHI, Tegiri wrote:
> >> Jan Hidders wrote:
> >>> Do you know of any results that might be interesting for database
> >>> theory and could not already be shown with good old set theory?
> >> The categorical sketches to use for universal view updatability:
> >>
> >> Michael Johnson and Robert Rosebrugh.
> >> Universal view updatability
> >
> > They claim to solve view updatability? OK, I have a table RealPeople
> > with one attribute Name and the view
> >
> > CDTPosters =
> > RealPeople
> > union
> > {(name=TeGiriNeNashi)}
> >
> > and a constraint
> >
> > RealPeople
> > intersect
> > {(name=TeGiriNeNashi)}
> > =
> > {}
> >
> > Is the CDTPosters view updatable?
>
> I like that example, but can you come up with one that doesn't involve a
> constraint? (I think constraints muddy the waters and at worst confuse
> us with un-related questions.)
I cannot get rid of the constraint completely, but can rewrite the problem to make it look "smaller":
select name, 'U' as typ from (
select name from RealPeople
union
select 'TeGiriNeNashi'
)
union
select name, 'I' as typ from (
select name from RealPeople
intersect
select 'TeGiriNeNashi'
)
check typ = 'U' Received on Tue Nov 07 2006 - 19:20:10 CET