Identity columns are columns that have unique values for every row in the table. Because those values confer uniqueness on every row, the system can use the values to identify each row in a table. When a column is defined as an identity column, Teradata Database automatically generates a unique numeric value for the column in every row that is added to the table.
Identity columns can be used to generate unique values for UPI, USI, and primary key columns. However, creating a UPI from combinations of frequently queried columns is preferable to adding identity columns to tables to serve this function.
For more information about indexes, see Teradata Database Indexes.