select d.dept_no,d.dept_name,count(s.salary) sum from departments d left join

dept_emp de on d.dept_no=de.dept_no

left join salaries s on de.emp_no = s.emp_no

group by d.dept_no order by dept_no asc

或

select d.dept_no,d.dept_name,count(s.salary) sum from (departments d left join dept_emp de on

d.dept_no =de.dept_no) left join

salaries s on de.emp_no = s.emp_no

group by d.dept_no