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Data & Analytics · Advanced

Superkey

Any set of one or more columns whose combined values uniquely identify each row, whether or not it is minimal.

Definition

A superkey guarantees uniqueness but may contain extra attributes. Removing those attributes until none can be dropped without losing uniqueness gives a candidate key. Superkeys are used in normalization theory, including the definition of Boyce-Codd normal form.

Example

{EmpID, Name} is a superkey because EmpID alone is already unique.

Exam tip

Every candidate key is a superkey, but not every superkey is a candidate key.

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