is there any performance overhead creating indexes on a table columns, whose data type is other than number or interger? i mean if we have a table Emp with the following structure and assume that eno, ename both will only accept unique values. in this case , what is the recommended way to create index? is it on eno or ename? i read that indexes on numbers will have better performance over the indexes, which are created on characters. could any body please explain the reason behind this.