596 Classes More Than 5 Students 超过5名学生的课
Description:
There is a table courses with columns: student and class
Please list out all classes which have more than or equal to 5 students.
Example:
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.
题目描述:
有一个courses 表 ，有: student (学生) 和 class (课程)。
请列出所有超过或等于5名学生的课。
示例 :
例如,表:
+---------+------------+
| student | class |
+---------+------------+
| A | Math |
| B | English |
| C | Math |
| D | Biology |
| E | Math |
| F | Computer |
| G | Math |
| H | Math |
| I | Math |
+---------+------------+
应该输出:
+---------+
| class |
+---------+
| Math |
+---------+
说明:
学生在每个课中不应被重复计算。
思路:
使用 GROUP BY和 HAVING条件, 用 DISTINCT筛选不重复的学生
代码:
MySQL:
SELECT
class
FROM
courses
GROUP BY
class
HAVING
COUNT ( DISTINCT student ) > 4
