select product_id,ifnull(round(sum(if_click)/count(id),3),0),ifnull(round(sum(if_cart)/sum(if_click),3),0),
  ifnull(round(sum(if_payment)/sum(if_cart),3),0),ifnull(round(sum(if_refund)/sum(if_payment),3),0) r
from tb_user_event
where date_format(event_time,'%Y-%m')='2021-10'
group by product_id
having r<=0.5
order by product_id;