Multiple indexes can be created on the same set of columns as long as some characteristic is different. Qualifying characteristics are:
- B-tree versus bitmap
- Different partitioning strategies
- Unique versus nonunique
Providing the capability to create multiple indexes on the same set of columns enables transparent and seamless application migrations without the need to drop an existing index and re-create it with different attributes.
SQL> CREATE INDEX emp_ind1 ON EMPLOYEE(EMPNO,EMPNAME);
SQL> CREATE BITMAP INDEX emp_ind2 ON EMPLOYEE (EMPNO, EMPNAME) INVISIBLE;