If you have a query returning many rows of data, and you want to perform another query on those rows, you can put the first query as a subquery in the FROM clause of the second query. The following statement shows you how to use a subquery as base table for the main query:

SQL> SELECT * FROM (

2 SELECT first_name, last_name, department_name

3 FROM employees e, departments d

4 WHERE e.department_id = d.department_id

5 ) WHERE department_name LIKE 'S%' ORDER BY last_name;

FIRST_NAME  LAST_NAME   DEPARTMENT_NAME

----------------- ---------------------- ---------------

Ellen   Abel    Sales

Sundar  Ande    Sales

Mozhe   Atkinson   Shipping

Amit   Banda   Sales

Elizabeth  Bates   Sales

Sarah   Bell    Shipping