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