What is a surrogate key, and why might it be used instead of a natural key?

• A. A surrogate key is a natural identifier derived from business meaning.
• B. A surrogate key is an artificial, usually numeric key used for stable identification; it avoids issues with natural keys that can change.
• C. A surrogate key is always a composite of several attributes.
• D. A surrogate key is used only for archival data.

Answer: (B)

A surrogate key is an artificial, usually numeric, identifier created solely to uniquely identify a record. It’s not derived from or tied to business data, and it’s typically generated by the database so it remains stable—never changing as other attributes of the row change.

This stability is the main reason to use a surrogate key instead of a natural key. Natural keys come from real-world attributes (like a customer email or ID) and can change, be large or complex, or even fail to remain unique across systems. A surrogate key stays small and fixed, making joins and indexing simpler and more efficient, and avoiding the need to update primary keys when business data changes. In practice, you often reserve the natural attributes as alternate keys with their own uniqueness constraints, while the surrogate key serves as the primary key for reliable, fast relationships.