On Tue, May 20, 2003 at 15:50:11 -0400,
Mark Wilson <mwilson13(at)cox(dot)net> wrote:
>
> As one example, a primary key with business meaning assures that one
> does not have duplicate records (if the data model is otherwise
> correct).
Unique isn't really good enough. You also want it to be defined for all
records and you don't want it to change.
I don't know about national ID numbers in the UK, but in the US it is
possible to change them, not everyone has one, and they aren't unique
(due to screwups - not intentionally).