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 grouping by employee name, as well as department and salary grade. That means you will return a row for every combination of employee name, department and salary grade in your dataset.

To ensure that you only return one row per department and salary grade, you will need to remove the employee name from the group by clause. This will enable you to find the maximum salary per grade and department, but not which employees have that salary - to do that, you need to join the results back to the employee table again, like so:

select e.ename, s.grade, d.dname, e.salary
from (select max(emp.salary) max_salary, 
             salgrade.grade,
             emp.deptno 
      from emp, salgrade
      WHERE emp.sal BETWEEN salgrade.losal AND salgrade.hisal
      group by salgrade.grade, dept.dname) s
     join emp e on e.salary = s.max_salary
     join dept d on e.deptno = d.deptno

Note that if multiple employees in the same department are earning the same maximum salary within their grade, then both employees will be returned - this should happen with FORD and SCOTT in RESEARCH.