题解 | #月均完成试卷数不小于3的用户爱作答的类别#

with cet_atc_uid as (
    select uid
    from exam_record
    join examination_info using(exam_id)
    group by uid,month(submit_time)
    having count(submit_time)>=3
)
# 使用with子查询得出符合条件的用户uid

select
    tag,
    count(start_time) as tag_cnt
from exam_record
left join examination_info using(exam_id)
where uid in (select uid from cet_atc_uid)
# 根据已有uid筛选
group by tag
# 测试代码的时候没有加tag分组，导致报错，后来知道如果select后面跟了非聚合和聚合就要用group by指明非聚合列
order by tag_cnt desc