[SQL]LeetCode596. 超過5名學生的課 | Classes More Than 5 Students

★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★
➤微信公衆號：山青詠芝（shanqingyongzhi）
➤博客園地址：山青詠芝（https://www.cnblogs.com/strengthen/）
➤GitHub地址：https://github.com/strengthen/LeetCode
➤原文地址：http://www.javashuo.com/article/p-xiwxiqow-me.html 
➤若是連接不是山青詠芝的博客園地址，則多是爬取做者的文章。
➤原文已修改更新！強烈建議點擊原文地址閱讀！支持做者！支持原創！
★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★

SQL架構

 1 Create table If Not Exists courses (student varchar(255), class varchar(255))
 2 Truncate table courses
 3 insert into courses (student, class) values ('A', 'Math')
 4 insert into courses (student, class) values ('B', 'English')
 5 insert into courses (student, class) values ('C', 'Math')
 6 insert into courses (student, class) values ('D', 'Biology')
 7 insert into courses (student, class) values ('E', 'Math')
 8 insert into courses (student, class) values ('F', 'Computer')
 9 insert into courses (student, class) values ('G', 'Math')
10 insert into courses (student, class) values ('H', 'Math')
11 insert into courses (student, class) values ('I', 'Math')

---

There is a table courses with columns: student and class

Please list out all classes which have more than or equal to 5 students.

For example, the table:

+---------+------------+
| student | class      |
+---------+------------+
| A       | Math       |
| B       | English    |
| C       | Math       |
| D       | Biology    |
| E       | Math       |
| F       | Computer   |
| G       | Math       |
| H       | Math       |
| I       | Math       |
+---------+------------+

Should output:

+---------+
| class   |
+---------+
| Math    |
+---------+ 

Note:
The students should not be counted duplicate in each course.

---

有一個courses 表 ，有: student (學生) 和 class (課程)。

請列出全部超過或等於5名學生的課。

例如,表:

+---------+------------+
| student | class      |
+---------+------------+
| A       | Math       |
| B       | English    |
| C       | Math       |
| D       | Biology    |
| E       | Math       |
| F       | Computer   |
| G       | Math       |
| H       | Math       |
| I       | Math       |
+---------+------------+

應該輸出:

+---------+
| class   |
+---------+
| Math    |
+---------+

Note:
學生在每一個課中不該被重複計算。

---

1465ms

1 # Write your MySQL query statement below
2 select class
3 from courses group by class having COUNT(DISTINCT student) >= 5

---

1479ms

1 # Write your MySQL query statement below
2 SELECT 
3     class
4 FROM
5     courses
6 GROUP BY class
7 HAVING COUNT(DISTINCT student)>=5