前面的sql case when 语法貌似有误 你 改成这样:
select a.*,ifnull(b.jan_num,0) from info a left join
(
select
mid,
sum(case when month(dtime)=1 then 1 else 0 end) jan_num
from signtime group by mid
) b on a.id = b.mid
//给出一月,其它月份的以此类推
select a.*,ifnull(b.jan_num,0) from info a left join
(
select
mid,
sum(case month(dtime)=1 when 1 else 0 end)jan_num
from signtime group by mid
)b on a.id = b.mid