What is a natural key?

A natural key is an identifier derived from real business data rather than generated solely by the database. Examples can include an ISO country code, a stable product code, or another business identifier that is guaranteed to be unique.

Natural keys can be meaningful, but they may be problematic if business rules allow them to change, if they are large, or if they contain multiple columns. Many production designs therefore use a surrogate primary key while enforcing the natural business identifier with a UNIQUE constraint.