select e1.emp_no,(s1.salary-e1.salary) as growth
from (select e.emp_no ,s.salary
from employees as e left join salaries as s on e.emp_no=s.emp_no
where e.hire_date=from_date ) as e1,
(select e.emp_no ,s.salary
from employees as e left join salaries as s on e.emp_no=s.emp_no
where e.hire_date<from_date and to_date='9999-01-01') as s1
where e1.emp_no=s1.emp_no
order by growth
不太懂题目的意思，是离职的才计算薪资涨幅吗？