【LeetCode】力扣刷题记录-第N高的薪水

表: Employee

+-------------+------+
| Column Name | Type |
+-------------+------+
| id          | int  |
| salary      | int  |
+-------------+------+
id 是该表的主键（列中的值互不相同）。
该表的每一行都包含有关员工工资的信息。

编写一个解决方案查询 Employee 表中第 n 高的 不同 工资。如果少于 n 个不同工资，查询结果应该为 null 。

查询结果格式如下所示。

示例 1:

输入: 
Employee table:
+----+--------+
| id | salary |
+----+--------+
| 1  | 100    |
| 2  | 200    |
| 3  | 300    |
+----+--------+
n = 2
输出: 
+------------------------+
| getNthHighestSalary(2) |
+------------------------+
| 200                    |
+------------------------+

示例 2:

输入: 
Employee 表:
+----+--------+
| id | salary |
+----+--------+
| 1  | 100    |
+----+--------+
n = 2
输出: 
+------------------------+
| getNthHighestSalary(2) |
+------------------------+
| null                   |
+------------------------+

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

CREATE FUNCTION getNthHighestSalary(N INT) RETURNS INT
BEGIN
  RETURN (
      # Write your MySQL query statement below.
      SELECT DISTINCT salary
      FROM Employee e1
      WHERE N - 1 = (
          SELECT COUNT(DISTINCT e2.salary)
          FROM Employee e2
          WHERE e2.salary > e1.salary
      )
  );
END

CREATE FUNCTION getNthHighestSalary(N INT) RETURNS INT
BEGIN
  RETURN (
      # Write your MySQL query statement below.
      SELECT DISTINCT salary
      FROM (
          SELECT salary, DENSE_RANK() OVER (ORDER BY salary DESC) as rnk
          FROM Employee
      ) ranked
      WHERE rnk = N
  );
END