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: <>

"DBMS_Plumber" <> wrote in message
> 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 - 11:16:28 CEST

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