题解 | #每月各旬有多少人练题#

select 
concat(
                CONCAT(left(event_date,4),'年'),
                CONCAT(mid(event_date,6,2),'月'),
                (case when day(event_date) between '01' and '09' then '上旬'
                         when day(event_date) between '10' and '19' then '中旬'
                         else '下旬'
                         end)) as dt_range,
                         count(distinct device_id) cnt
from  question_practice_detail
group by dt_range
order by substr(dt_range,6,2) desc,cnt desc