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。
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 | +---------+
Note:
学生在每个课中不应被重复计算。
答案:
去重
select class, count(student) from courses GROUP BY class HAVING count(DISTINCT student) >=5
未去重:
select class, count(class) from courses GROUP BY class HAVING count(class) >=5