[LeetCode] 596. Classes More Than 5 Students_Easy tag:SQL

转载于 2018-08-20 03:03:00 发布 · 77 阅读

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原文链接：http://www.cnblogs.com/Johnsonxiong/p/9503511.html

本文介绍了一种使用SQL查询的方法，来找出那些报名学生数量大于或等于5人的课程班级。通过GROUP BY和HAVING子句结合使用DISTINCT关键字去除重复的学生记录，确保统计数据的准确性。

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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.

Code #用distinct是因为有可能有学生多次选了该门课

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

转载于:https://www.cnblogs.com/Johnsonxiong/p/9503511.html