Re: I have read tons of theory...but still...one question

"Lemming" <thiswillbounce_at_bumblbee.demon.co.uk> wrote in message news:8ft0n0p93s2q4o6vu05l19thp2qve9pcnm_at_4ax.com...
> On Fri, 15 Oct 2004 00:52:18 -0400, "Kostas" <noemail_at_noemail.net>
> wrote:
>
>>Many thanks to anyone who can clue me in,
>
> This is not an answer, but a question.
>
> Somewhere in this thread someone said to use the phone number as the
> primary key. Or maybe it was a differnet thread, and that's why I
> can't find it :) Anyway ...
>
> What happens in such a scheme if two people have the same phone
> number?

Here is the answer (please note I am a novice only compared to the folks that frequent this group so it would be better if someone else validated my answer).

The phone number is unique. If our database had only phones we are fine as we are.
If, on the other hand (and most expected case), we also hold information about people that have phone numbers then we will also have a second entity PERSON.
As such, PHONE becomes a weak entity because the existence of a particular phone implies the existence of a particular person that owns it.

In logical design this would mean that the primary key for PHONE is now the combination of PersonID and PhoneNumber fields, which is always unique, so we are fine because the PersonID would be different for the 2 people with the same phone number.

>
> What happens if one person has two or more phone numbers?

Again, no problem. Different PhoneNumber this time. The combination PersonID, PhoneNumber still remains unique.

Cheers!
Konstantinos

> I'm fairly certain I've missed the point once again.
>
> Lemming
> --
> Curiosity *may* have killed Schrodinger's cat.
Received on Sat Oct 16 2004 - 04:22:44 CEST