请输入任务描述
select 销量,库存,库存-销量 as 净库存
from 表
select a.产品编码,a.库存-b.销量 as 剩余库存 (select 产品编码,sum(库存 ) as 库存 from 库存 group by 产品编码)a left join (select 产品编码,sum(销量) as 销量 from 订单 group by 产品编码) b on a.产品编码=b.产品编码