先考虑用group by找到各个部门的部门号和相应最高工资

with (select e1.dept_no, max(s1.salary)
from dept_emp e1 join salaries s1
on e1.emp_no = s1.emp_no
group by e1.dept_no) as t1

然后同样通过连接获取部门、员工和薪资的联系，等值选取即可

select e.dept_no, e.emp_no, s.salary as `maxSalary`
from dept_emp e join salaries s
on e.emp_no = s.emp_no
where (e.dept_no, s.salary) in t1
order by e.dept_no