SQL query with correlated subquery in where clause - sql

Question

I am fighting with a SQL.
The task is to write max(EMP.SAL) for each project (PROJ_EMP.PROJNO)
I have 3 tables.
Table PROJ which keep data about projects:
PROJ.PROJNO | PROJ.NAME
------------+-------------
1 | PROJECT1
2 | PROJECT2
3 | PROJECT3
Table EMP for employees data:
EMP.EMPNO | EMP.NAME | EMP.SALARY
----------+----------+------------
1000 | name1 | 4000
1001 | name2 | 2000
1002 | name3 | 3000
1003 | name4 | 6000
1004 | name5 | 1000
And Table PROJ_EMP for connecting these projects with employees:
PROJ_EMP.EMPNO | PROJ_EMP.PROJNO
---------------+----------------
1000 | 1
1001 | 1
1002 | 2
1003 | 2
1004 | 3
Such I mentioned at the beginning post: I am trying to write max(EMP.SAL)for each project using a correlated subquery in where clause so the desired result should be:
PROJ_EMP.PROJNO | EMP.EMPNO | EMP.SAL
----------------+-----------+---------
1 | 1000 | 4000
2 | 1003 | 6000
3 | 1004 | 1000
I don't have any working result however my SQL query closed to aim looks:
SELECT EMP.EMPNO, EMP.SAL, PROJ_EMP.PROJNO
FROM EMP, PROJ_EMP
WHERE EMP.EMPNO = PROJ_EMP.EMPNO
AND EMP.SAL = (SELECT MAX(EMP.SAL)
FROM EMP, PROJ_EMP p_e
WHERE EMP.EMPNO = PROJ_EMP.EMPNO
AND PROJ_EMP.PROJNO = p_e.PROJNO)
GROUP BY
PROJ_EMP.PROJNO, EMP.SAL, EMP.EMPNO
ORDER BY
PROJ_EMP.PROJNO, EMP.SAL DESC
By the result are not like I expected. Can you help me? Thank you fo any help in advance

Answer 1

Learn to use proper, explicit, standard JOIN syntax. I think you are trying to write:
SELECT e.EMPNO, e.SAL, pe.PROJNO
FROM EMP e JOIN
PROJ_EMP pe
ON e.EMPNO = pe.EMPNO
WHERE EMP.SAL = (SELECT MAX(EMP.SAL)
FROM EMP e2 JOIN
PROJ_EMP pe2
ON e2.EMPNO = pe2.EMPNO
WHERE pe2.PROJNO = pe.PROJNO
)
ORDER BY pe.PROJNO, e.SAL DESC ;

Answer 2

You can apply inner join among three tables and filter by max analytic function partitioned by project number and ordered by descending salary to determine the max salaries for each project number :
select projno, empno, salary
from
(
select p.projno, e.empno, e.salary,
max(e.salary) over (partition by p.projno order by e.salary desc) as max_salary
from proj p
join proj_emp pe on pe.projno = p.projno
join emp e on e.empno = pe.empno
)
where salary = max_salary;
Demo