LeetCode Second Highest Salary

Problem

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

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

即找到第二大的元素。没有返回null。

MySQL

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

分析

通过LIMIT OFFSET找到第二个元素。DISTINCT是为了排除两个最大值的情况。嵌套是为了解返回null的情况。另一种办法是使用IFNULL函数。