Question

我有这样的表格：

Products
ID | Name 
1  | Prod1
2  | Prod2

Product_history

ID | Product_id | quantity | order_id | date
1  | 1          | 10       | 1        | 2014-01-01 10:00:00
2  | 1          | 11       | 1        | 2014-01-01 11:00:00
3  | 1          | 20       | 2        | 2014-01-01 09:00:00
4  | 2          | 50       | 2        | 2014-01-01 09:00:00

我无法创建查询女巫将只返回最后日期的每个订单数量总和的所有产品。在这个例子中，我想返回：

product_id | quantity
1          | 31 (11 + 20)
2          | 50

你能帮助我吗？

Answer 1

select p1.product_id, sum(p1.quantity)
from product_history p1
join
(
  select product_id, max(date) as date
  from product_history
  group by product_id
) p2 on p1.product_id = p2.product_id and p1.date = p2.date
group by p1.product_id

Answer 2

以下是使用not exists的方法：

select ph.product_id, sum(ph.quantity)
from product_history ph
where not exists (select 1
                  from product_history ph2
                  where ph2.order_id = ph.order_id and
                        ph2.product_id = ph.product_id and
                        ph2.date > ph.date
                 )
group by ph.product_id;

如果您的表很大，则需要product_history(order_id, product_id, date)上的综合索引来提高性能。

MySql查询获取只有一个连接行的行

2 个答案: