题解 | #月均完成试卷数不小于3的用户爱作答的类别#

• 原来group by 之前可以用where语句？ ！ 我一直以为用了group by 就只能用having。现在纠正过来这个知识点
• 正确理解：当月均完成试卷数”不小于3的用户

count(exam_id) / count(distinct DATE_FORMAT (start_time, "%Y%M")) >= 3

原来上一次刷题竟是上个月月底，隔了10来天没刷又手生了。现在赶上！这个月中旬，争取把这套进阶题库刷完！！加油！

select
    tag,
    count(tag) as tag_cnt
from
    exam_record
    left join examination_info using (exam_id)
where
    uid in (
        select
            uid
        from
            exam_record
        where
            submit_time is not null
        group by
            uid
        having
            count(exam_id) / count(distinct DATE_FORMAT (start_time, "%Y%M")) >= 3
    )
group by
    tag
order by
    tag_cnt desc