Ahh. i finally get it. Very good example. Thanks. now it makes sense.
"Niall Litchfield" <n-litchfield_at_audit-commission.gov.uk> wrote in message
news:3bd59d16$0$238$ed9e5944_at_reading.news.pipex.net...
> "ed zappulla" <zappullae_at_rcn.com> wrote in message
> news:9r42mp$jv0$1_at_bob.news.rcn.net...
> > many countries do not have postal codes. Ireland for one.
> >
> > country, state, city is the proper key with a null state being valid.
> >
> >
> Didn't know that which given my name is somewhat embarrassing <vbg>.
>
> if you have two records with the same country and city and a null state
then
> logically they could be the same place and hence violate the uniqueness
> requirement for a primary key, or they might not be the same place and so
> not violate the uniqueness requirement. who can tell? Certainly not oracle
> which is why a primary key must be not null and unique.
>
>
> --
> Niall Litchfield
> Oracle DBA
> Audit Commission UK
>
>
Received on Thu Oct 25 2001 - 11:48:43 CDT
