select t1.data_date,
t1.platform,
count(distinct t1.user_id),
count(distinct case when t1.data_date=date_sub(t2.data_date,interval 1 days then t1.user_id else null end)/count(distinct t1.user_id)
from new_tabel as t1, active_table as t2
where t1.user_id=t2.user_id
group by t1.data_date,t1.platform；

不晓得对不对。。。。