編寫一個 SQL 查詢，獲取 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查詢應該返回200 作為第二高的薪水。如果不存在第二高的薪水，那麼查詢應返回 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;