Re: Curious SQL question

From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Sat, 06 Jan 2007 19:53:10 GMT
Message-ID: <G6Tnh.41409$cz.608841@ursa-nb00s0.nbnet.nb.ca>

Lennart 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.
>

>> 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.

AND and/or OR require NOT to express all the truth tables NAND gets by all on its own
NOR gets by all on its own Received on Sat Jan 06 2007 - 13:53:10 CST