原文链接: https://leetcode-cn.com/problems/second-highest-salary

英文原文

Table: Employee

+-------------+------+
| Column Name | Type |
+-------------+------+
| id          | int  |
| salary      | int  |
+-------------+------+
id is the primary key column for this table.
Each row of this table contains information about the salary of an employee.

 

Write an SQL query to report the second highest salary from the Employee table. If there is no second highest salary, the query should report null.

The query result format is in the following example.

 

Example 1:

Input: 
Employee table:
+----+--------+
| id | salary |
+----+--------+
| 1  | 100    |
| 2  | 200    |
| 3  | 300    |
+----+--------+
Output: 
+---------------------+
| SecondHighestSalary |
+---------------------+
| 200                 |
+---------------------+

Example 2:

Input: 
Employee table:
+----+--------+
| id | salary |
+----+--------+
| 1  | 100    |
+----+--------+
Output: 
+---------------------+
| SecondHighestSalary |
+---------------------+
| null                |
+---------------------+

中文题目

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

通过代码

官方题解

方法一：使用子查询和 LIMIT 子句

算法

将不同的薪资按降序排序，然后使用 LIMIT 子句获得第二高的薪资。

[7gHRPQAW-MySQL]
SELECT DISTINCT
    Salary AS SecondHighestSalary
FROM
    Employee
ORDER BY Salary DESC
LIMIT 1 OFFSET 1

然而，如果没有这样的第二最高工资，这个解决方案将被判断为 “错误答案”，因为本表可能只有一项记录。为了克服这个问题，我们可以将其作为临时表。

[Z4dXjTB5-MySQL]
SELECT
    (SELECT DISTINCT
            Salary
        FROM
            Employee
        ORDER BY Salary DESC
        LIMIT 1 OFFSET 1) AS SecondHighestSalary
;

方法二：使用 IFNULL 和 LIMIT 子句

解决 “NULL” 问题的另一种方法是使用 “IFNULL” 函数，如下所示。

[UF7BUDgS-MySQL]
SELECT
    IFNULL(
      (SELECT DISTINCT Salary
       FROM Employee
       ORDER BY Salary DESC
        LIMIT 1 OFFSET 1),
    NULL) AS SecondHighestSalary

统计信息

通过次数	提交次数	AC比率
266358	750650	35.5%

提交历史

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