Re: Curious SQL question

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.

/Lennart Received on Sat Jan 06 2007 - 11:49:26 CST