select s1.emp_no,(s1.salary-s2.salary) as growth
from 
(select emp_no,salary from salaries where to_date='9999-01-01') s1---------在职员工涨薪后工资表
join
(select s.emp_no,salary from employees e join salaries s  
on e.emp_no=s.emp_no and e.hire_date=s.from_date) s2-----------员工原有工资表
on s1.emp_no=s2.emp_no
order by growth

注意事项

1.用where to_date='9999-01-01' 既可以筛选出在职员工，又能筛选出调整后的工资，一举两得

2.s1和s2内连接后，将emp_no中非在职的部分也剔除了

3.做减法时，两列数据需一一对应