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Data & Analytics · Intermediate

Alternate Key

A candidate key that was not chosen as the primary key, usually enforced with a UNIQUE constraint.

Definition

Alternate keys still uniquely identify rows and are often used for lookups by business users. They are declared with UNIQUE constraints so the database still rejects duplicates.

Example

Email UNIQUE in a Users table whose primary key is UserID.

Exam tip

If a question asks how to enforce uniqueness on a non-PK column, the answer is a UNIQUE constraint, i.e. an alternate key.

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