Re: Curious SQL question

"Lennart" <Erik.Lennart.Jonsson_at_gmail.com> wrote in message news:1168105671.732196.161730_at_38g2000cwa.googlegroups.com...
>
> Walt wrote:
> [...]
> >
> > XOR (A,B) = MINUS ( UNION (A,B), INTERSECTION (A,B))
> >
> > Is this true? Is it a working definition?
>
> That is one definition of symmetric difference, and I assume Bob choose
> that name because of another definition
>
> { x | x belongs to A XOR x belongs to B }
>
> For the record, I don't understand the purpose of giving well defined
> operations new names, that at best will be confusing in its new
> context.
>
> > Can it be transformed so that
> > MINUS is defined in terms of XOR, UNION, and INTERSECTION?
> >
>
> Why not go all the way, XOR, OR and AND :-). Hmm, I cant come up with
> an expression for this without using NOT. Either its not possible, or
> I'm to stupid. I suspect the latter.

I'm going to start a new topic. This looks interesting.

> /Lennart
>
Received on Sat Jan 06 2007 - 21:12:28 CET