Re: How to ensure only one of two sets of optional information?

From: Marshall Spight <mspight_at_dnai.com>
Date: Fri, 19 Dec 2003 22:11:00 GMT
Message-ID: <UHKEb.432884$275.1302916@attbi_s53>

"Bob Badour" <bbadour_at_golden.net> wrote in message news:vO6dncxSy8Cxwn6iRVn-iw_at_golden.net...
> > I could do it with a database constraint. Is there a structural
> > way to do it that I'm not seeing? If I have to use a constraint,
> > is there a canonical form for this particular example? It seems
> > like a common thing to want to do, but I haven't come across
> > how to address the subtype-data-exclusion issue anywhere.
>
> Make account type part of the account candidate key and include a constant
> attribute in the referencing relations.

OMG that is *such* a cool solution! Thanks!

Does SQL have the concept of a "constant attribute?" Coincidentally I've actually been thinking lately that such a thing would be useful. Generically speaking it's just a type constraint and probably not anything all that special.

Marshall Received on Fri Dec 19 2003 - 16:11:00 CST