【leetcode Database】176. Second Highest Salary

題目：

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 second highest salary is 200. If there is no second highest salary, then the query should return null.

解析：本題採用子查詢的方法來做。先取出薪水最高的，然後在所有比最高薪水低的薪水中選取最高的即可。代碼如下：

# Write your MySQL query statement below
SELECT MAX(Salary) as SecondHighestSalary FROM Employee WHERE Salary < (SELECT MAX(Salary) FROM Employee);