牛客网数据库SQL实战21—— 查找所有员工自入职以来的薪水涨幅情况

牛客网数据库SQL实战21—— 查找所有员工自入职以来的薪水涨幅情况

题目描述

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

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,
PRIMARY KEY (`emp_no`));

CREATE TABLE `salaries` (
`emp_no` int(11) NOT NULL,
`salary` int(11) NOT NULL,
`from_date` date NOT NULL,
`to_date` date NOT NULL,
PRIMARY KEY (`emp_no`,`from_date`));

输入描述:

无

输出描述:

emp_no	growth
10011	0
省略	省略
10010	54496
10004	34003

我的解答

select t1.emp_no,(t1.sTo - t2.sHire) as growth 
from 
(
    select e.emp_no,s.salary as sTo 
    from employees e
    left join  salaries s 
    on e.emp_no = s.emp_no 
    where s.to_date='9999-01-01'
) as t1,
(
    select e.emp_no,s.salary as sHire 
    from employees e
    left join  salaries s 
    on e.emp_no = s.emp_no 
    and s.from_date = e.hire_date
) as t2 
where t1.emp_no=t2.emp_no
order by growth; 

此题思路如下：

1. 找出每个员工当前工资
2. 找出每个员工入职时的工资
3. 结合找出growth并通过growth排序

我觉得最好的答案

本题思路是先分别用两次LEFT JOIN左连接employees与salaries，建立两张表，分别存放员工当前工资（sCurrent）与员工入职时的工资（sStart），再用INNER JOIN连接sCurrent与sStart，最后限定在同一员工下用当前工资减去入职工资。
方法一：内层用LEFT JOIN，外层用INNER JOIN（内层也可以改用 INNER JOIN）

SELECT sCurrent.emp_no, (sCurrent.salary-sStart.salary) AS growth
FROM (SELECT s.emp_no, s.salary FROM employees e LEFT JOIN salaries s ON e.emp_no = s.emp_no WHERE s.to_date = '9999-01-01') AS sCurrent
INNER JOIN (SELECT s.emp_no, s.salary FROM employees e LEFT JOIN salaries s ON e.emp_no = s.emp_no WHERE s.from_date = e.hire_date) AS sStart
ON sCurrent.emp_no = sStart.emp_no
ORDER BY growth

方法二：内外都层用FROM并列查询

SELECT sCurrent.emp_no, (sCurrent.salary-sStart.salary) AS growth
FROM (SELECT s.emp_no, s.salary FROM employees e, salaries s WHERE e.emp_no = s.emp_no AND s.to_date = '9999-01-01') AS sCurrent,
(SELECT s.emp_no, s.salary FROM employees e, salaries s WHERE e.emp_no = s.emp_no AND s.from_date = e.hire_date) AS sStart
WHERE sCurrent.emp_no = sStart.emp_no
ORDER BY growth

最简洁的方法：

select a.emp_no, (b.salary - c.salary) as growth
from
    employees as a
    inner join salaries as b
    on a.emp_no = b.emp_no and b.to_date = '9999-01-01'
    inner join salaries as c
    on a.emp_no = c.emp_no and a.hire_date = c.from_date
order by growth asc