LeetCode 177. Nth Highest Salary

题目

Write a SQL query to get the nth highest salary from the Employee table.

+----+--------+
| Id | Salary |
+----+--------+
| 1  | 100    |
| 2  | 200    |
| 3  | 300    |
+----+--------+

For example, given the above Employee table, the nth highest salary where n = 2 is 200. If there is no nth highest salary, then the query should return null.

+------------------------+
| getNthHighestSalary(2) |
+------------------------+
| 200                    |
+------------------------+

题目大意

写一个SQL函数来从表中获得第n 个最高工资

解题思路

SQL 函数

CREATE FUNCTION getNthHighestSalary(N INT) 
RETURNS INT  -- 返回数据类型
BEGIN -- 函数体开始
-- 声明 : 变量 类型
DECLARE  M INT;
-- 变量赋值
SET M=N-1;

  RETURN (
       SELECT DISTINCT Salary FROM Employee ORDER BY Salary DESC LIMIT M,1);
 );  -- 返回这条语句的结果
END

SQL 语句并没有什么好说的,这里要详细学习一个新的概念,SQL 中的函数

MySQL 5.7 CREATE FUNCTION Syntax for User-Defined Functions

MySQL 自定义函数详解

详见下文
MySQL 自定义函数详解