176. 第二高的薪水

編寫一個 SQL 查詢，擷取 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查詢應該傳回 200 作為第二高的薪水。如果不存在第二高的薪水，那麼查詢應傳回 null。

+---------------------+

| SecondHighestSalary |

| 200 |

來源：力扣（LeetCode）

連結：https://leetcode-cn.com/problems/second-highest-salary

開始學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;