先把order表聚一下在连接,否则同个款型有多个记录

SELECT style_id,
      round(sum(sales_num)/
      (sum(inventory)-sum(sales_num))*100,2),
      round(100*sum(GMV)/sum(tag_price*(inventory)),2)
from
product_tb left JOIN 
(select item_id,sum(sales_num) as sales_num,
sum(sales_price) as GMV from sales_tb 
where month(sales_date)=11
GROUP by item_id) tmp
using(item_id) 
GROUP BY style_id