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 | +---------------------+
方法一：
# Write your MySQL query statement below select IFNULL((select Distinct Salary from Employee order by Salary DESC limit 1,1),null) as SecondHighestSalary
方法二：
# Write your MySQL query statement below select max(Salary) as SecondHighestSalary from Employee where Salary<(select max(Salary) from Employee)