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$cz.608841_at_ursa-nb00s0.nbnet.nb.ca>
>
> That is one definition of symmetric difference, and I assume Bob choose
> that name because of another definition
>
> { x | x belongs to A XOR x belongs to B }
>
> For the record, I don't understand the purpose of giving well defined
> operations new names, that at best will be confusing in its new
> context.
>
>
>
> Why not go all the way, XOR, OR and AND :-). Hmm, I cant come up with
> an expression for this without using NOT. Either its not possible, or
> I'm to stupid. I suspect the latter.
Date: Sat, 06 Jan 2007 19:53:10 GMT
Message-ID: <G6Tnh.41409$cz.608841_at_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 - 20:53:10 CET