Re: What predicates the following relation represents

From: Mikito Harakiri <mikharakiri_at_iahu.com>
Date: Wed, 31 Mar 2004 12:25:49 -0800
Message-ID: <YYFac.34$rc5.83_at_news.oracle.com>


"Eric Kaun" <ekaun_at_yahoo.com> wrote in message news:HgFac.574$ho2.515_at_newssvr32.news.prodigy.com...
> A primary key is an arbitrarily-chosen candidate key, and is downplayed by
> Date as being of little importance. UNIQUE is a SQL artifact, but could be
> interpreted as meaning candidate key. Candidate keys identify functional
> dependencies.

If I filter out nonmathematical (read non informational) part of your paragraph, it's just reduces to

"keys identify functional dependencies"

which is rather loose and informal way to say that given a relation with signature <A,B,C> and functional dependency A->A,B,C then, A is a key.

> It's hard to say
> without understanding the requirements, but is certainly suspicious.

Parts database is defined in Date's textbook. Wait a minute, did he miss the requitrements? Received on Wed Mar 31 2004 - 22:25:49 CEST

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