Nth Highest Salary

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

思路：熟悉limit 用法；求offset 1之后的row count1，就是第二大，求offset n - 1之后的第一个就是第N大；注意set一定要写在return前面；

CREATE FUNCTION getNthHighestSalary(N INT) RETURNS INT
BEGIN
DECLARE M INT;
SET M = N - 1;
  RETURN (
    select distinct Salary from Employee Order by Salary desc limit M, 1
  );
END