题解 | #月均完成试卷数不小于3的用户爱作答的类别#
重点是月平均完成考试的数目大于等于三。
select t2.tag,count(t1.exam_id) tag_cnt
from exam_record t1
left join examination_info t2
on t1.exam_id = t2.exam_id
where uid
in (select uid from exam_record
where submit_time is not null
group by uid having count(score)/count(DISTINCT DATE_FORMAT(start_time,"%Y%m"))>=3
)
group by tag
order by tag_cnt desc
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