# 177. Nth Highest Salary

### 題目敘述

SQL Schema >

``````Create table If Not Exists Employee (Id int, Salary int)
Truncate table Employee
insert into Employee (id, salary) values ('1', '100')
insert into Employee (id, salary) values ('2', '200')
insert into Employee (id, salary) values ('3', '300')
``````

Table: `Employee`

``````+-------------+------+
| Column Name | Type |
+-------------+------+
| id          | int  |
| salary      | int  |
+-------------+------+
id is the primary key column for this table.
Each row of this table contains information about the salary of an employee.
``````

Write an SQL query to report the `nth` highest salary from the `Employee` table. If there is no `nth` highest salary, the query should report `null`.

The query result format is in the following example.

Example 1:

``````Input:
Employee table:
+----+--------+
| id | salary |
+----+--------+
| 1  | 100    |
| 2  | 200    |
| 3  | 300    |
+----+--------+
n = 2
Output:
+------------------------+
| getNthHighestSalary(2) |
+------------------------+
| 200                    |
+------------------------+
``````

Example 2:

``````Input:
Employee table:
+----+--------+
| id | salary |
+----+--------+
| 1  | 100    |
+----+--------+
n = 2
Output:
+------------------------+
| getNthHighestSalary(2) |
+------------------------+
| null                   |
+------------------------+
``````

### 解法解析

#### 程式範例

##### SQL
``````CREATE FUNCTION getNthHighestSalary(N INT)

RETURNS INT

BEGIN
DECLARE M INT;

SET
M = N -1;

RETURN (
# Write your MySQL query statement below.
SELECT
IFNULL(
(
SELECT
DISTINCT salary
FROM
Employee
ORDER BY
salary DESC
LIMIT
1 OFFSET M
),
NULL
)
);

END
``````