Re: How could I model this relationship?

On Wed, 26 Jun 2002 10:39:27 +0100
"Stu" <smcgouga_at__at_yaho.com_> wrote:

> Just thinking: What if not every customer was a company. i.e. every
> customer is either a company OR a persons name (persons name is the only
> details we would have.)
>
> cheers
> stu

Is person name always unique?
I know tens John Smith;)
You should use an unique index for customers. In ER model it can be represented via Class Hierarchy Customers cover both companies and clients. In tables:
table customers (id_customer, other attr) table companies (id_company, other atrr) table clients (id_client, other attr)
foreing key companies (id_company) references customers (id_customer) foreing key clients (id_client) references customers (id_customer) table business (id_company, id_customer) foreign key business (id_company) references companies (id_company) foreing key business (id_customer) references customers (id_customer)

Regards,
Pavel                                            Received on Wed Jun 26 2002 - 12:39:20 CEST