随便写的一大段竟然很快就通过了。。。。select device_id, concat( concat(year(event_date),'年'), concat(substr(event_date,6,2),'月') ) as ym, count(device_id) as cnt from (select *, (case when month(event_date) in (1,3,5,7,8,10,12) then 31 when month(event_date) in (4,6,9,11) then 30 else 28 end ) as last_day from questio...