MySQL 依赖另外一个统计出来数据更新表数据的范例

MySQL 依赖另外一个统计出来数据更新表数据的范例：

update goods g,(SELECT goods_id ,sum(product_number) as num     
FROM `products`     
group by goods_id) b     
set goods_number = num     
where g.goods_id = b.goods_id