with
    c as (
        select
            a.goods_id,
            a.user_id,
            a.sales_num,
            b.goods_price,
            a.sales_num * b.goods_price as total
        from
            sales_tb a
            left join goods_tb b using (goods_id)
    )
select
    round(sum(total), 3) as sales_total,
    round(sum(total) / count(distinct user_id), 3) as pre_trans
from
    c