超過5名學生的課
阿新 • • 發佈:2018-12-21
有一個courses
表 ,有: student (學生) 和 class (課程)。
請列出所有超過或等於5名學生的課。
例如,表:
+---------+------------+ | student | class | +---------+------------+ | A | Math | | B | English | | C | Math | | D | Biology | | E | Math | | F | Computer | | G | Math | | H | Math | | I | Math | +---------+------------+
應該輸出:
+---------+ | class | +---------+ | Math | +---------+
Note:
學生在每個課中不應被重複計算。
第一種:
select classfrom courses group by class having count(distinct student)>=5
執行程式碼:
第二種:
select class from (select class,count(distinct student) as nums from courses group by class)b where nums>=5
輸出: