https://www.nowcoder.com/practice/fc7344ece7294b9e98401826b94c6ea5?tpId=82&tqId=29773&rp=0&ru=/ta/sql&qru=/ta/sql/question-ranking
查詢所有員工自入職以來的薪水漲幅情況，給出員工編號emp_noy以及其對應的薪水漲幅growth，並按照growth進行升序
CREATE TABLE employees (
emp_no int(11) NOT NULL,
birth_date date NOT NULL,
first_name varchar(14) NOT NULL,
last_name

建立兩張表，分別存放員工當前工資和員工入職工資，然後將兩表並列查詢。

select
 
 a.emp_no,(b.salary-a.salary) as growth
from (select e.emp_no,s.salary 
      from salaries s,employees e 
      where s.emp_no=e.emp_no 
      and s.from_date=e.hire_date) as a,
     (select e.emp_no,s.salary
      from salaries s,employees e
      where s.emp_no=e.emp_no
      and s.to_date='9999-01-01'
 
) as b
where a.emp_no=b.emp_no
order by growth