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                   |
+------------------------+

題目翻譯

要寫一個 SQL 可以接收 n 然後取出第 n 高的 salary。

解法解析

這題就是上一題 176. Second Highest Salary 的延伸。但是這題其實有個問題，就是如果當 n 是負值的話目前的解法都會出錯。他應該要限定一下 n 的範圍，或是在 testcase 應該要加上測試負值。

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