If a table does not have one of the preceding types of row identifiers, or if you prefer those identifiers not to be used, you can define a substitute key if the table has columns that always contain unique values. You define this substitute key by including a KEYCOLS clause within the Extract TABLE and the Replicat MAP parameters. The specified key will override any existing primary or unique key that Oracle GoldenGate finds. For more information, see Reference for Oracle GoldenGate.