leetcode 596 BUG笔记

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.

大概考察group by 但是第一次我交代码wa了 看错误提示才发现，测试样例中有重复记录 所以要加DISTINCT

answer

select class
from courses
group by class
having count(DISTINCT student)>=5