Question

If I used an Index column in a query which returns all the Rows, is it advantageous to use the Index column in the where clause ?

For eg. select * from table1 where Salary > 1;

If the salary of all the employees is greater than 1, is it advantageous to use the Index column in the where clause ?

Are Indexed a big overhead while inserting if the Database is most likely to be used as above ?

Answer 1

Indexes are useless when You perform full scans without ORDER BY . Oracle index organized table,Postgresl cluster table, MySQL (InnoDB) PRIMARY KEY clustered index: give big performance for ORDER BY.

http://dev.mysql.com/doc/refman/5.1/en/innodb-index-types.html

“Are Indexed a big overhead while inserting if the Database is most likely to be used as above ?”
If index fit into RAM everything is ok.