Re: Thinking about MINUS
From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Sun, 07 Jan 2007 16:48:33 GMT
Message-ID: <Bv9oh.41744$cz.613288_at_ursa-nb00s0.nbnet.nb.ca>
>
> One of a couple of reasons this topic intrigues me is that certain
> scenarios aren't closed for operations in Codd's framework, eg., the
> case when two operands share an attribute name that has different types.
> I realize that a whole sub-industry has been built to deal with
> problems like this (based on various design disciplines, knowingly or
> unknowingly, I don't know), so many people would say I'm silly to
> wonder, but I can't help it.
Date: Sun, 07 Jan 2007 16:48:33 GMT
Message-ID: <Bv9oh.41744$cz.613288_at_ursa-nb00s0.nbnet.nb.ca>
paul c wrote:
> Walt wrote:
> ...
>
>> Either NOR or NAND are enough to bootstrap to the rest of it, provided >> you >> make one little extension to them: >> >> NOR or NAND with only one operand is NOT. >> >> I don't know where it leads regarding database, either. Just a random >> thought.
>
> One of a couple of reasons this topic intrigues me is that certain
> scenarios aren't closed for operations in Codd's framework, eg., the
> case when two operands share an attribute name that has different types.
> I realize that a whole sub-industry has been built to deal with
> problems like this (based on various design disciplines, knowingly or
> unknowingly, I don't know), so many people would say I'm silly to
> wonder, but I can't help it.
Wouldn't one end up with a resulting attribute defined as a union-type in a relation with no rows? Received on Sun Jan 07 2007 - 17:48:33 CET