select 
x.dept_no,
x.emp_no,
x.salary as maxSalary
FROM
(SELECT
de.dept_no,
de.emp_no,
s.salary,
row_number()over(partition by de.dept_no order by s.salary desc)as mm
from dept_emp de
LEFT JOIN salaries s on s.emp_no = de.emp_no)x
where x.mm =1
order by x.dept_no