SQL Not A Single Group Group Function

Question

Okay guys here is the question. I have to list the department ID, department name, count of sales reps, and average commission rate for each department. Also I need to Group by

Answer 1

Add a group by.

SELECT DE.Dept_ID as Dept_ID, Dept_Name, 
  COUNT(SR.Sales_Rep_ID) as NumOfSalesR, 
  Comm_Rate as AVGCOM 
FROM DEPT_arb DE, SALES_REP_arb SR, COMMISSION_arb C
WHERE DE.Dept_ID = SR.Dept_ID 
   AND Comm_Rate = (SELECT AVG(Comm_Rate) 
                    FROM COMMISSION_arb 
                    WHERE SR.Comm_Class = C.Comm_Class)
GROUP BY DE.Dept_ID, Dept_Name, Comm_Rate