Oracle SQL sample database

Question

I\'m trying to learn Oracle SQL by database Supplied by it. I found somewhere tasks to be done. Database structure is supplied by Oracle:

CREATE TABLE EMP
(EMPNO         


        

Answer 1

You are not filtering your query this is why you have all the employees displayed.

This would filter the employees that earn less than the max for their dept/grade:

SELECT ename, salgrade.grade, dept.dname
  FROM emp, salgrade, dept
 WHERE emp.sal BETWEEN salgrade.losal AND salgrade.hisal
   AND emp.deptno = dept.deptno
   AND emp.sal = (SELECT MAX(sal)
                    FROM emp emp_in, salgrade grade_in
                   WHERE emp_in.sal BETWEEN grade_in.losal AND grande_in.hisal
                     AND emp_in.deptno = emp.deptno
                     AND grade_in.losal = salgrade.losal)

You will still find duplicates because for instance, two people in sales earn the max salary for grade 2 (both Martin and Ward earn 1250). Either this is acceptable or you need some other criteria to only select one of them.

You can use the row_number analytic function to ensure that only one row is returned by grade/dept (note that Oracle will select arbitrarily one row when there are duplicates) :

SELECT * FROM (
  SELECT ename, salgrade.grade, dept.dname,
         row_number() OVER (PARTITION BY dept.deptno, salgrade.grade 
                            ORDER BY emp.sal DESC) rnk
    FROM emp, salgrade, dept
   WHERE emp.sal BETWEEN salgrade.losal AND salgrade.hisal
     AND emp.deptno = dept.deptno
) WHERE rnk = 1;

ENAME       GRADE DNAME          RNK
---------- ------ -------------- ---
MILLER          2 ACCOUNTING       1 
CLARK           4 ACCOUNTING       1 
KING            5 ACCOUNTING       1 
ADAMS           1 RESEARCH         1 
FORD            4 RESEARCH         1 
JAMES           1 SALES            1 
MARTIN          2 SALES            1 
ALLEN           3 SALES            1 
BLAKE           4 SALES            1