Re: Base Normal Form

From: Gene Wirchenko <genew_at_ucantrade.com.NOTHERE>
Date: Tue, 12 Jul 2005 09:19:36 -0700
Message-ID: <bsq7d1pbpoabrugf2bep07tg56cl54k6k7@4ax.com>

On 12 Jul 2005 02:57:08 -0700, "dawn" <dawnwolthuis_at_gmail.com> wrote:

[snip]

>It is easy enough to model a database relation with a set theory
>relation, so this is not a problem, but when db relational theorists
>get all preachy on this unordered point, it amuses me.

     Be careful about that amusement. Sometimes, it is because the other people know more about the situation than you do. Surely, you have heard the saying "Ignorance is bliss."?

[snip]

>So, remind me, what precisely is the problem with ordering the
>attributes in relations? It results in ... because ... ???

     If you say that the ordering is significant, then
          (a,b,c)
and
          (a,c,b)

are different. If you go purely by the name, they are the same. (I have omitted the types for simplicity. Assume that they are the same.)

     This does not look like much, but consider a join. Now, you have to define which order the columns are in the join. Make sure you do it right, or you could end up with A join B and B join A resulting in different orderings.

[snip]

     This is rather basic stuff, Dawn. You claim to have studied the material. Is your axe not ground enough yet?

Sincerely,

Gene Wirchenko Received on Tue Jul 12 2005 - 11:19:36 CDT