Re: Curious SQL question

On Jan 6, 9:47 am, "Lennart" <Erik.Lennart.Jons..._at_gmail.com> wrote:
> 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.

For me, the relationship between the boolean operations in set builder notation, as above, and the associated relational operations has been key in building an understanding of those relational operators.
So much so that I now write natural join as "&" and inner union as "|" in my personal notation.

Marshall Received on Sat Jan 06 2007 - 19:23:16 CET