Primary Key Constraints

• A set of fields is a superkey for a relation if:

  • No two distinct tuples have the same values in all fields of the superkey

• A superkey is a (candidate) key if :

  • No proper subset of it is a superkey

• If there’s ɭ candidate key for a relation, one of the keys is chosen (by DBA) to be the primary key.

• E.g., sid is a key for Students. (What about name?) The set {sid, gpa} is a superkey.

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