select a.emp_no, `salary_end`-`salary_start` growth
from
(select e.emp_no, salary as salary_start
from employees e
left join salaries s
on e.emp_no = s.emp_no and e.hire_date = s.from_date) a
left join 
(select e.emp_no, salary as salary_end
from employees e
left join salaries s
on e.emp_no = s.emp_no and to_date = '9999-01-01') b
on a.emp_no = b.emp_no
where `salary_end`-`salary_start` is not null
order by growth