LeetCode: 176. Second Highest Salary

题目描述

Write a SQL query to get the second highest salary from the ​​Employee​​ table.

+----+--------+
| Id | Salary |
+----+--------+
| 1  | 100    |
| 2  | 200    |
| 3  | 300    |
+----+--------+

For example, given the above ​​Employee​​​ table, the query should return ​​200​​ as the second highest salary. If there is no second highest salary, then the query should return null.

+---------------------+
| SecondHighestSalary |
+---------------------+
| 200                 |
+---------------------+

解题思路

首先找到最高薪水，然后将最高薪水表和薪水表连接。在新表中 ​​Salary < SecondHighestSalary​​ 的最大值就是所求的第二高薪水。

AC 代码

# Write your MySQL query statement below
select 
MAX(Salary) as SecondHighestSalary  
from 
(select MAX(Salary) as HighestSalary from Employee) as HS, -- 最高薪水表
Employee as E 
where HS.HighestSalary > E.Salary;