我要评论编写一个 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 |
+---------------------+
代码1：
# Write your MySQL query statement below
select (select Salary from Employee where Salary < (select Salary from Employee order by Salary DESC limit 1) order by Salary DESC limit 1) as SecondHighestSalary代码2：
# Write your MySQL query statement below
select (select distinct Salary from Employee order by Salary DESC limit 1,1) as SecondHighestSalary
# select (select distinct Salary from Employee order by Salary DESC limit 1 offset 1) as SecondHighestSalary代码3：
# Write your MySQL query statement below
select ifnull((select distinct Salary from Employee order by Salary DESC limit 1,1), NULL) as SecondHighestSalary
# select ifnull((select distinct Salary from Employee order by Salary DESC limit 1 offset 1), NULL) as SecondHighestSalary笔记：
代码3是常见模板。不过，似乎IFNULL(([SQL Query Set]), NULL)是多余的。就目前看来，更像是“画蛇添足”：一个 SQL Query Set 只有 非NULL 和 NULL 两种情况。
本文地址：https://blog.csdn.net/qq_21264377/article/details/107924737
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