Re: A pk is *both* a physical and a logical object.

From: Roy Hann <specially_at_processed.almost.meat>
Date: Sun, 15 Jul 2007 10:16:28 +0100
Message-ID: <cpKdnYV__O9zeATbnZ2dnUVZ8t-nnZ2d@pipex.net>

"DBMS_Plumber" <paul_geoffrey_brown_at_yahoo.com> wrote in message news:1184480376.333327.38370_at_i13g2000prf.googlegroups.com...
> As a footnote, Quel had/has a primary key / foreign key concept.

When you say Quel, are you referring to a particular implementation of it? Ingres Quel is probably the most widely used implementation and I have just glanced at the latest manual to refresh my memory, and I see no mention of primary or foreign keys at all.

> It wasn't just the SQL community who thought picking a single key was
> a practical and useful idea.

Which just goes to show that lots of people doing a silly thing doesn't constitute a sensible basis for doing it.

> And Jan's absolutely correct. There is no theoretical justification
> for the idea of a primary key as distinct from a simple candidate key
> at all.

Not only is there no theoretical justification for it, it is sometimes a nuisance in practice that one cannot have a referential integrity constraint referring to one of the other candidate keys.

Roy Received on Sun Jul 15 2007 - 04:16:28 CDT