## Try using TABLE JOINS in place of EXISTS


SELECT EMP_NAME 
FROM   EMP E
WHERE  EXISTS ( SELECT 'X' 
                FROM   DEPT
                WHERE  DEPT_NO  = E.DEPT_NO
                AND    DEPT_CAT = 'A');



## To improve performance, specify:

SELECT EMP_NAME
FROM   DEPT D, 
       EMP  E
WHERE  E.DEPT_NO  = D.DEPT_NO
AND    D.DEPT_CAT = 'A';