Inline view in Oracle

An inline view is a SELECT statement in the FROM-clause of another SELECT statement. In-line views are commonly used simplify complex queries by removing join operations and condensing several separate queries into a single query.

Example inline view:

SELECT * 
  FROM ( SELECT deptno, count(*) emp_count
         FROM emp
         GROUP BY deptno ) emp,
       dept
 WHERE dept.deptno = emp.deptno;

Another good example of an inline view is:

SELECT a.last_name, a.salary, a.department_id, b.maxsal
  FROM employees a,
       ( SELECT department_id, max(salary) maxsal
         FROM employees
         GROUP BY department_id ) b
 WHERE a.department_id = b.department_id
   AND a.salary = b.maxsal;

The above query display the employees who earn the highest salary in each department.

Note:-Please comment and reply me.