176. 第二高的薪水

编写一个 SQL 查询，获取 Employee 表中第二高的薪水（Salary） 。

+----+--------+
| Id | Salary |
+----+--------+
| 1 | 100 |
| 2 | 200 |
| 3 | 300 |
+----+--------+
例如上述 Employee 表，SQL查询应该返回 200 作为第二高的薪水。如果不存在第二高的薪水，那么查询应返回 null。

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

来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/second-highest-salary

开始学SQL

# Write your MySQL query statement below
SELECT
    (SELECT DISTINCT
            Salary
        FROM
            Employee
        ORDER BY Salary DESC
        LIMIT 1 OFFSET 1)as SecondHighestSalary
;

# Write your MySQL query statement below
select max(Salary ) SecondHighestSalary 
from Employee 
where Salary < (select max(Salary) from Employee )

select (select distinct Salary from Employee order by Salary desc limit 1 offset 1) as SecondHighestSalary;