select round(sum(total_amount)/ count(order_id),1) avg_amount, round(avg(cost),1) avg_cost from (select a.order_id order_id, total_amount, sum(price*cnt)-total_amount cost from tb_order_detail a left join tb_order_overall b on a.order_id=b.order_id left join tb_product_info c on a.product_id=c.produ...