数据库SQL实战-18.查找员工编号emp_no为10001其自入职以来的薪水salary涨幅值growth

思路是查找出日期最大的薪水以及入职时候（日期最小）的薪水就是薪水的涨幅值，日期最大和最小通过对日期排序即可实现。

select (
(select salary from salaries where emp_no=10001 order by to_date desc limit 1)-
    (select salary from salaries where emp_no=10001 order by to_date limit 1)
) as growth