LeetCode.176 Second Highest Salary （Limit偏移量运用）

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题目：

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

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

分析：

# Write your MySQL query statement below#给定工资表，查找工资第2的数据，如果不存在该数据，则返回null#先找出k个大的数据，之后在该批数据中查找最小的#防止只有一个数据的情况select max(emp.salary) as 'SecondHighestSalary'from(select salaryfrom employeegroup by salaryorder by salary desclimit 1,1) as emp;#科教篇 limit来表示偏移量，可以直接取第2大的数据# SELECT * FROM table  LIMIT [offset,] rows | rows OFFSET offset; #limit start,OFFSET offset # 入门篇# SELECT * FROM table LIMIT 0,10;//检索记录行1-10 # 进阶篇# SELECT * FROM table LIMIT 2,10;//检索记录行3-13# SELECT * FROM table LIMIT 5,20;//检索记录行6-25 # 高级篇# SELECT* FROMtable LIMIT 5,-1;//检索记录行6到结尾数据# SELECT* FROMtable LIMIT 0,-1;//检索全部记录# SELECT * FROM table LIMIT 5;   //检索前 5 个记录行

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