surrogate key

database A unique primary key generated by the RDBMS

that is not derived from any data in the database and whose

only significance is to act as the primary key.

A surrogate key is frequently a sequential number (e.g. a

Sybase "identity column") but doesn't have to be. Having

the key independent of all other columns insulates the

database relationships from changes in data values or database

design and guarantees uniqueness.

Some database designers use surrogate keys religiously

regardless of the suitability of other candidate keys.

However, if a good key already exists, the addition of a

surrogate key will merely slow down access, particularly if it

is indexed.

Compare: intelligent key.

(1999-12-07)