题目：

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 （注:可能有employees表和salaries表里存在记录的员工，有对应的员工编号和涨薪记录，但是已经离职了，离职的员工salaries表的最新的to_date!='9999-01-01'，这样的数据不显示在查找结果里面）

CREATE TABLE `employees` (
`emp_no` int(11) NOT NULL,
`birth_date` date NOT NULL,
`first_name` varchar(14) NOT NULL,
`last_name` varchar(16) NOT NULL,
`gender` char(1) NOT NULL,
`hire_date` date NOT NULL, --  '入职时间'
PRIMARY KEY (`emp_no`));
CREATE TABLE `salaries` (
`emp_no` int(11) NOT NULL,
`salary` int(11) NOT NULL,
`from_date` date NOT NULL, --  '一条薪水记录开始时间'
`to_date` date NOT NULL, --  '一条薪水记录结束时间'
PRIMARY KEY (`emp_no`,`from_date`));

程序：

SELECT b.emp_no, (b.salary - a.salary) AS growth
FROM
(SELECT c.emp_no, d.salary
FROM employees AS c INNER JOIN salaries AS d
ON c.emp_no = d.emp_no
WHERE c.hire_date = d.from_date) AS a
INNER JOIN
(SELECT c.emp_no, d.salary
FROM employees AS c INNER JOIN salaries AS d
ON c.emp_no = d.emp_no
WHERE d.to_date = '9999-01-01') AS b
ON a.emp_no = b.emp_no
ORDER BY growth ASC