select b.emp_no,a.emp_no manager_no, b.salary, a.salary manager_salary
from
(select dm.dept_no, dm.emp_no, s.salary
from dept_manager dm
left join 
salaries s
on dm.emp_no=s.emp_no) a # 经理工资
inner join
(select de.emp_no,de.dept_no,s.salary
from dept_emp de
left join
salaries s
on de.emp_no=s.emp_no) b #员工工资 
on a.dept_no=b.dept_no
and a.salary<b.salary

分别写出经理信息和员工信息，然后连接两个查询，控制连接条件便可以求解