LeetCode 596. Classes More Than 5 Students

LeetCode 596. Classes More Than 5 Students

题目

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.

题目大意,找出选修人数超过5门的学生,每门课的学生不应该重复计算

解题思路

使用 group by 分组后 count(distinct 学生) 大于5的即为需要展示的内容

SELECT class FROM courses GROUP BY class  HAVING count(DISTINCT student) >= 5;