[리트코드] 596. Classes More Than 5 Students

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       리트코드 Problems / https://leetcode.com/problemset/all/  임을 밝힙니다.

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■ 문제

https://leetcode.com/problems/classes-more-than-5-students/description/

Classes More Than 5 Students - LeetCode

 

Table: Courses

+-------------+---------+
| Column Name | Type    |
+-------------+---------+
| student     | varchar |
| class       | varchar |
+-------------+---------+
(student, class) is the primary key column for this table.
Each row of this table indicates the name of a student and the class in which they are enrolled.

 

Write an SQL query to report all the classes that have at least five students.

Return the result table in any order.

The query result format is in the following example.

 

Example 1:

Input: 
Courses table:
+---------+----------+
| student | class    |
+---------+----------+
| A       | Math     |
| B       | English  |
| C       | Math     |
| D       | Biology  |
| E       | Math     |
| F       | Computer |
| G       | Math     |
| H       | Math     |
| I       | Math     |
+---------+----------+
Output: 
+---------+
| class   |
+---------+
| Math    |
+---------+
Explanation: 
- Math has 6 students, so we include it.
- English has 1 student, so we do not include it.
- Biology has 1 student, so we do not include it.
- Computer has 1 student, so we do not include it.

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■ 풀이

  문제 요구사항  

최소 5명 이상의 학생이 있는 클래스를 모두 출력해라

> class 컬럼 기준으로 그룹핑 한 후

   (집계함수) COUNT가 5 이상인 class를 출력해야하므로

    HAVING절을 사용한다.

SELECT class
 FROM Courses
 GROUP BY 1
 HAVING COUNT(*) >= 5;