根據一張表的內容去更新另外一張表的內容

有兩個表
1, out_proudctlist(出庫物品清單)
id outlist_id product_id out_num
1 out1 11 2
2 out1 12 5
3 out2 11 2
.......


2, product(物品資訊)
id product_id product_name stock_num
1 11 牛奶 20
2 12 涼茶 20

update t
set stock_num=t.stock_num-A.out_num
from product t
join (
select product_id
,sum(out_num) as 'out_num'
from out_proudctlist
group by product_id
)A on t.product_id=A.product_id