Classes More Than 5 Students

• LeetCode: Classes More Than 5 Students

• Problem:

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.

• Analysis:

The problem doesn't say that students should be distinct.

So, we should use GROUP BY and COUNT(DISTINCT column)

• SQL:

# Write your MySQL query statement below
SELECT class FROM courses GROUP BY class HAVING COUNT(DISTINCT student)>4