select 
t.dept_no,
t.emp_no,
t.salary
from
(select 
e.emp_no,
e.dept_no,
s.salary,
row_number() over(partition by e.dept_no order by s.salary desc) as ranking
from dept_emp e left join salaries s 
on e.emp_no=s.emp_no) t
where t.ranking=1