SELECT department_id ,  AVG(salary) FROM employees WHERE commission_pct != "null" GROUP BY department_id
display the average salary of employees for each department who gets a commission percentage.
SELECT department_id , AVG ( salary ) FROM employees WHERE commission_pct ! = `` null '' GROUP BY department_id
select department_id , avg ( salary ) from employees where commission_pct ! = value group by department_id
display the average salary of employees for each department who gets a commission percentage .