max函数：
select
t1.dept_no,
t1.emp_no ,
max(t2.salary) maxSalary
from
(
select
emp_no,
dept_no
from dept_emp
)t1
left join
(
select
salary,
emp_no
from salaries
)t2
on
t1.emp_no = t2.emp_no
group by t1.dept_no
order by dept_no