Identifying candidate keys and primary keys

I'm still confused with the concepts of candidate keys and primary key. We have a patient medication form from an hospital with these:

Heading: Patient number, Full name, Bed number, Ward number, Ward name.
Then a table with this columns: drug number, name, description, dosage, method of admin, units per day, start date, finish date.

I have to find all the candidate keys and primary keys. I think candidate keys are the minimal superkeys.

I have found {Patient number, Ward number, Ward name}. I have excluded {Patient number, Ward number, Ward name, Full name} and {Patient number, Ward number, Ward name, Full name, Bed number} which are also superkeys but contain more attributes.

This means that I have found only one candidate key, and this is also the primary key I have found (a composite).

Since the question was "identify all the candidate keys" I thought maybe I dont really understand the concepts...

thanks for any help. Received on Sun Apr 13 2008 - 11:29:27 CEST