select
round(price_sum * 1.0, 3) sales_total
,round(price_sum / num * 1.0, 3) per_trans
from(
    select 
    sum(sales_num) sales_sum
    ,sum(sales_num * goods_price) price_sum
    ,count(distinct user_id) num
    from sales_tb s
    join goods_tb g
    on s.goods_id = g.goods_id 
) t