Nested Sub Query

=>    A query embedded in another Query or Sub Query.
=>    Queries can be nested upto 255 level.

    Syntax:
    =>    Select ....
                 ( select ....
                     ( select ....


    Examples:
    1. Select 2nd max salary ?
    =>    Select MAX( sal ) from emp where sal < ( Select MAX( sal ) from emp );

    2. Find the Location of the employee who is earning 2nd max sal ?
    =>    Select loc from dept where deptno in ( select deptno from emp where sal = (
        Select MAX( sal ) from emp where sal < ( Select MAX( sal ) from emp ) ) );