Re: Enforcing functional dependecy constraints
Date: Wed, 07 Dec 2005 14:34:04 GMT
Message-ID: <wpClf.507$nm.373_at_newsread2.news.atl.earthlink.net>
"x" <x_at_not-exists.org> wrote in message
news:dn1j2m$fpo$1_at_domitilla.aioe.org...
But before we move from relations to SQL, maybe we could discuss a little
normalization:
You could decompose the relation R(A,B,C) into two relations S(A,C) and
T(C,B).
> Hi !
>
> Since this is a database theory group and I'm bored by the null and 3vl
> threads I ask yet another elementary question:
>
> Suppose you have this relation R(A,B,C) with the following functional
> dependencies AB->C and C->B.
> What is the best way to implement this in available SQL DBMS in your
opinion
> ?
>
> Regards,
> x
>
I'm not sure what you mean by "best". If it's my opinion of "what's best",
I'm going to dodge the question by giving the universal answer: "It
depends".
Please bear with me for presenting relation T in a curious order. These two can be recombined, unless I miss my guess, back into R(A,B,C) without loss. I think S and T are better than R from the point of view of hermful redundancy and update anomalies. Is this relevant to your original question?
Do you have a different answer? Received on Wed Dec 07 2005 - 15:34:04 CET