[mysql] LeetCode 176.Second Highest Salary

176.Second Highest Salary

https://leetcode.com/problems/second-highest-salary/

문제설명

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 second highest salary from the Employee table. If there is no second 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    |
+----+--------+
Output:
+---------------------+
| SecondHighestSalary |
+---------------------+
| 200                 |
+---------------------+

Example 2:

Input:
Employee table:
+----+--------+
| id | salary |
+----+--------+
| 1  | 100    |
+----+--------+
Output:
+---------------------+
| SecondHighestSalary |
+---------------------+
| null                |
+---------------------+

---

풀이

# Write your MySQL query statement below
SELECT max(salary) AS SecondHighestSalary
FROM Employee
WHERE salary not in (SELECT max(salary) FROM Employee);

다른풀이

SELECT max(salary) as SecondHighestSalary 
FROM Employee
WHERE salary <> (select max(salary) from Employee);

+++ not in, <>