题解 | #月均完成试卷数不小于3的用户爱作答的类别#

-- 1.统计出当月完成次数>=3的有哪些用户（去重）

-- 2.统计这些用户作答了哪些试卷（去重）

-- 3.统计这些试卷的作答次数


select t3.tag,count(t2.exam_id) tag_cnt
from exam_record t2, examination_info t3
where
t2.uid in (
    select distinct t1.uid t1_uid
    from 
    (
        select uid , count(uid) cnt_uid
        from exam_record
        where score is not null
        group by left(start_time , 7) , uid
        having cnt_uid >= 3
    ) t1

) 
and t2.exam_id = t3.exam_id
group by t2.exam_id
order by tag_cnt desc