Surrogate

A surrogate represents an object in the database itself. The surrogate is internally generated by the system and is invisible to the user or application.
In a current database, the surrogate key can be the primary key, generated by the database management system and not derived from any application data in the database. 

Approaches to generating surrogates include:

• Universally Unique Identifiers (UUIDs)
• Globally Unique Identifiers (GUIDs)
• Object Identifiers (OIDs)
• Sybase or SQL Server identity column IDENTITY OR IDENTITY(n,n)
• Oracle SEQUENCE
• PostgreSQL or IBM Informix serial
• MySQL AUTO_INCREMENT
• AutoNumber data type in Microsoft Access
• AS IDENTITY GENERATED BY DEFAULT in IBM DB2
• Identity column (implemented in DDL) in Teradata