select s1.emp_no,s1.salary-s2.salary growth from 
(select emp_no,salary from salaries where to_date='9999-01-01' group by emp_no) s1,
(select emp_no,salary from salaries where to_date<>'9999-01-01' group by emp_no) s2
where s1.emp_no=s2.emp_no
order by growth asc;