select date, concat(round(order_num/visit_num*100,1),'%') cr 
from
(select date(order_time) date,count(distinct o.user_id) order_num
from order_tb o 
group by date(order_time)) t1
join
(select date(visit_time) date,count(distinct v.user_id) visit_num
from visit_tb v 
group by date(visit_time)) t2 using(date)
order by date;
先乘100再保留1位小数还挺重要的，之前写的一个逻辑也是对的，主要是保留位数这里出了问题