Database designers frequently define multiple secondary indexes on a table.
For example, the following statements define two secondary indexes on the EMPLOYEE table:
CREATE INDEX (department_number) ON EMPLOYEE; CREATE INDEX (job_code) ON EMPLOYEE;
The WHERE clause in the following query specifies the columns that have the secondary indexes defined on them:
SELECT last_name, first_name, salary_amount FROM employee WHERE department_number = 500 AND job_code = 2147;
Whether the Optimizer chooses to include one, all, or none of the secondary indexes in its query plan depends entirely on their individual and composite selectivity.
For more information on multiple and composite secondary index access, and other aspects of index selection, see Database Design, B035-1094.