21.查找所有员工自入职以来的薪水涨幅情况

查找所有员工自入职以来的薪水涨幅情况，给出员工编号emp_no以及其对应的薪水涨幅growth，并按照growth进行升序

select b.emp_no,(b.salary-a.salary) as growth
from 
(select e.emp_no,s.salary
from employees e left join salaries  s on e.emp_no=s.emp_no
and e.hire_date=s.from_date)a -- 入职工资表
inner join 
(select e.emp_no,s.salary
from employees e left join salaries  s on e.emp_no=s.emp_no
where s.to_date='9999-01-01')b -- 现在工资表
on a.emp_no=b.emp_no
order by growth