What is the difference between a superkey, candidate key, and a primary key in a normalized...

What is the difference between a superkey, candidate key, and a primary key in a normalized database?

Expert Solution

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Super Key: An attribute or set of attributes that uniquely identifies a tuple within a relation

Candidate key: A super key such that no proper subset is a super key within the relation

Primary key: The candidate key that is selected to identify tuples uniquely within the relation, the candidate keys which are not selected as PKs are called "Alternate keys"

Example: Consider a Relation or Table R1. Let A,B,C,D,E are the attributes of this relation.

R(A,B,C,D,E)
A→BCDE This means the attribute 'A' uniquely determines the other attributes B,C,D,E.
BC→ADE This means the attributes 'BC' jointly determines all the other attributes A,D,E in the relation.

Primary Key :A
Candidate Keys :A, BC
Super Keys : A,BC,ABC,AD

ABC,AD are not Candidate Keys since both are not minimal super keys.

venereology answered 3 months ago

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