leetcode 596 BUG筆記

 

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 可是第一次我交代碼wa了 看錯誤提示才發現，測試樣例中有重複記錄 因此要加DISTINCT

answer 

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