LeetCode 177. Nth Highest Salary

https://leetcode.com/problems/nth-highest-salary/description/

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

---

 Create table If Not Exists Employee (Id int, Salary int);
 Truncate table Employee;
 insert into Employee (Id, Salary) values ('', '');
 insert into Employee (Id, Salary) values ('', '');
 insert into Employee (Id, Salary) values ('', '');

 CREATE FUNCTION getNthHighestSalary(N INT) RETURNS INT
 BEGIN
 DECLARE M INT;
 SET M = N - 1;
   RETURN (
       # Write your MySQL query statement below.
       SELECT
         (SELECT Salary
         FROM Employee
         ORDER BY Salary DESC
         LIMIT M, 1) AS getNthHighestSalary
   );
 END