LeetCode-Nth Highest Salary

Nth Highest Salary

##题目

####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.

##解题思路
该题是找到表中第n大的元素，这里通过排序后，使用limit进行选去，这里需要注意的是，如果不加SET M=N-1;,将LIMIT M, 1改为LIMIT N-1, 1则会出错，原因是由于mysql有值的限制，而对预先定义的变量除外，详见Why using LIMIT N-1,1 will cause error。

##算法代码
代码采用mysql实现：

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

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