Surrogatnyckel

Surrogatnyckel, in Swedish database terminology, refers to the concept known in English as a surrogate key. It is an artificial unique identifier used as the primary key in a relational database table. It has no intrinsic meaning to users and is typically generated by the database, such as an auto-incrementing integer or a globally unique identifier (GUID/UUID). Its main role is to serve as a stable, simple, and efficient identifier for records, decoupled from the actual business data stored in the table.

Properties: a surrogatnyckel is unique and immutable (usually not updated), and is not derived from business attributes. It is used as the primary key and as a foreign key in related tables to establish relationships. Because it is decoupled from business data, it remains stable even if business attributes change.

Advantages: it improves key stability when business identifiers may change; it avoids issues with composite keys or changing natural keys; it often produces smaller, fixed-length keys that speed up index lookups and joins; and it simplifies data integration from multiple sources.

Common implementations: numeric auto-increment (IDENTITY), sequences, or fixed-length UUIDs. In some designs, a surrogatnyckel is the only key, while in others it is complemented by one or more natural keys used for data validation or external references.

Trade-offs: introduces an extra column and a potential need to maintain additional business keys or constraints; may require additional joins to access business attributes; carries no business meaning, which can affect data readability.

Usage considerations: typically recommended when natural keys are large, composite, or subject to change, or when data from multiple sources must be merged consistently.