【Leetcode_MySQL】596. Classes More Than 5 Students

計算學生人數大於或等於 5 的科目。

leetcode 題目在這:https://leetcode.com/problems/classes-more-than-5-students/

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.

MySQL 解答:

# Write your MySQL query statement below
SELECT class FROM courses 
GROUP BY class
HAVING count(DISTINCT student)>=5

根據同樣的 class(GROUP BY class),再計算學生人數大於或等於 5 的科目(count(DISTINCT student)>=5)。

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