LeetCode_177 Nth Highest Salary

177. Nth Highest Salary

Write a SQL query to get the n^th highest salary from the Employee table.

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

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

+————————+
| getNthHighestSalary(2) |
+————————+
| 200 |
+————————+

解答：和上一题查询第二高薪是一个套路，取第N个数就可以了，需要注意的是OFFSET是传入的参数，需要减去1，SQL语句中不能直接运算，要先定义一个局部变量，将偏移先减去1:

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

总结，对空集合继续进行查询，或者函数运算操作，返回NULL。