Re: Primary Key: Maximun number columns exceeded?

Kelly,

the point with super/subtype is that they have the same primary key. The primary key do not grow as you add subtypes. I.e., you could have a supertype vehicle, and subtypes car, lorry etc. They would all have 'Registration_id' as primary key, even the supertype. The primary key of the super type would not be (Registration_id_car, Registration_id_lorry).

But when you add a car to your database, you will have to insert it into the supertype table Vehicle first, after that you can insert it into the subtype table Car.

To me it seems like your primary key for all the tables could be: ADDRESS_ID, LISTING_NUMBER, SECTION_NUMBER, PAGE_NUMBER, BOOK_NUMBER, PUB_DATE, TYPE
Maybe.

Regards,
Njål

--
Njål A. Ekern
n.a.ekern_at_usit.uio.no