Re: thinking about UPDATE

From: Mikito Harakiri <mikharakiri_at_iahu.com>
Date: Fri, 23 Jul 2004 11:41:28 -0700
Message-ID: <C9dMc.34$pk.55@news.oracle.com>

"Marshall Spight" <mspight_at_dnai.com> wrote in message news:OzaMc.12304$eM2.4222_at_attbi_s51...
> (Are there other tricks we can play to constrain the cardinality of a
> relation? Can we constrain the cardinality to exactly 1? 1 or more?)

Interestingly, MVFD with empty antecedent claims something about cardinality as well. For example,

{} -> {X} | {Y,Z}

says that cardinality of the XYZ relation is multiple of cardinaities of its projections to X and YZ. Unfortunately, this feature is too weak to resolve your question, as both 0*0=0 and 1*1=1 hold:-( Received on Fri Jul 23 2004 - 13:41:28 CDT