oj-sql

题目

596. 超过5名学生的课

思路

1. 先groupby，再直接having；
2. groupby之后求count，子查询筛选cnt；

solution

groupby & having

select class from Courses
group by class
having count(distinct student)>=5;

groupby & subquery

select class
from (
         select class,count(distinct student) cnt
         from Courses
         group by class
     ) t
where cnt>=5;