-- 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