leetcode-database-177. 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.

题意：查询第n高的记录，如果没有请返回null

思路：按照salary排正序，使用limit挑选出第N高

最终sql：

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