[SQL] LeetCode 176. 第二高的薪水 - [Easy]

176. 第二高的薪水

题目

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                 |
+---------------------+

---

SQL架构：

Create table If Not Exists Employee (Id int, Salary int);
Truncate table Employee;
insert into Employee (Id, Salary) values ('1', '100');
insert into Employee (Id, Salary) values ('2', '200');
insert into Employee (Id, Salary) values ('3', '300');

---

解题语句：

方法一：LIMIT

SELECT
	IFNULL( ( SELECT DISTINCT Salary FROM Employee ORDER BY Salary DESC LIMIT 1 OFFSET 1 ), NULL ) AS SecondHighestSalary;
	

方法二：MAX ()

SELECT
	MAX( Salary ) AS SecondHighestSalary 
FROM
	Employee 
WHERE
	Salary < ( SELECT MAX( Salary ) FROM Employee );