SELECT d.dept_no,d.dept_name,COUNT(d.dept_name) sum
FROM (SELECT c.dept_no,s.salary
    FROM dept_emp c RIGHT JOIN salaries s on c.emp_no=s.emp_no) b 
    LEFT JOIN departments d on b.dept_no=d.dept_no
    GROUP BY d.dept_no
    ORDER BY d.dept_no ASC;