Getting column ambiguously defined error in an SQL query

Question

SELECT MAX(EMP.SAL),DEPT.DNAME
FROM EMP
JOIN DEPT
ON EMP.DEPTNO=DEPT.DEPTNO
GROUP BY DEPT.DNAME
ORDER BY DEPTNO ASC;

I was trying to print the max salary of the employees from emp table by grouping them by the name of the department which I reference from DEPT table as Department name is not defined in EMP table so I just wanted to print department name instead of department number (DEPTNO) which is defined in EMP table. I'm new with DBMS commands help me with this

Answer 1

You should not be getting an ambiguous column but an undefined column error.

If you want to order by the department number, you should include that in the GROUP BY :

SELECT MAX(EMP.SAL), DEPT.DNAME
FROM EMP JOIN
     DEPT
     ON EMP.DEPTNO = DEPT.DEPTNO
GROUP BY DEPT.DNAME, DEPT.DEPTNO
ORDER BY DEPTNO ASC;

This should be the same result -- assuming two different departments don't have the same name.

You can also use an aggregation function:

SELECT MAX(EMP.SAL), DEPT.DNAME
FROM EMP JOIN
     DEPT
     ON EMP.DEPTNO = DEPT.DEPTNO
GROUP BY DEPT.DNAME
ORDER BY MAX(DEPTNO) ASC;

The ORDER BY should only use expressions and columns that are available after the aggregation.