title: Database index on a column with duplicate values
body: <p>If there is a table containing details of employees including a column Gender whose value can be either M/F. Now would it make sense to create an index on this column, would it make the search faster? Logically if we fire a select statement with where clause containing Gender as the column, it should cut down the search time by half. But I have heard that this kind of index will not help and would be actually ignored by the Database Optimizer while executing the query. But I am not getting why? Can somebody please explain? </p>