LeetCode: 176. Second Highest Salary

LeetCode: 176. Second Highest Salary
タイトルの説明
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                 |
+---------------------+

問題を解く構想.
まず、最高賃金を見つけて、最高賃金表と給与表を接続します.新しい表のSalary < SecondHighestSalaryの最大値は、求めた2番目の高い給料です.
ACコード

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