Question

我有两张桌子。一个表名为Shopper，看起来像

SHOPPER_ID | SHOPPER_NAME | 
-------------------------
1          | Marianna     | 
2          | Jason        |

另一个名为Order的表具有订单上的日期等信息

ORDER_ID | SHOPPER_ID | DATE
----------------------------------
1        | 1          | 08/09/2012
2        | 1          | 08/08/2012

现在我想通过SHOPPER_ID进行连接两个表和组的查询，因为一个购物者可以有多个订单，我想根据DATE值选择最新的订单。

我的查询如下：

Select * from Shopper as s join Order as o 
on s.SHOPPER_ID = o.SHOPPER_ID 
group by s.SHOPPER_ID

现在查询错误，因为我不知道如何应用过滤器来获取最新订单。提前谢谢！

Answer 1

我建议使用子选择：

Select s.SHOPPER_ID, s.SHOPPER_NAME, o.MAX_DATE
  from Shopper s
  INNER join (SELECT SHOPPER_ID, MAX(DATE) AS MAX_DATE
                FROM ORDER
                GROUP BY SHOPPER_ID) o 
    on s.SHOPPER_ID = o.SHOPPER_ID

祝你好运。

Answer 2

简单方法是使用row_number查找最新订单

<强> SQL Fiddle Demo

SELECT *
FROM 
     (SELECT S.*,
             O.[ORDER_ID], O.[DATE],
             ROW_NUMBER() OVER ( PARTITION BY S.SHOPPER_ID
                                 ORDER BY [DATE] DESC) as rn
      FROM Shopper S
      JOIN Orders O
        ON S.SHOPPER_ID = O.SHOPPER_ID
     ) T
WHERE rn = 1

Answer 3

您需要一个子查询来获取每个购物者的最后一个订单，然后将其与购物者和订单表一起加入以获取购物者的名称和订单ID

SELECT ss.SHOPPER_ID, ss.SHOPPER_NAME, oo.ORDER_ID LAST_ORDER
FROM (SELECT o.SHOPPER_ID, MAX(o.DATE) [DATE]
      FROM Shopper s
      INNER JOIN Order o
      ON s.SHOPPER_ID = o.SHOPPER_ID
      GROUP BY o.SHOPPER_ID) mo
INNER JOIN Shopper ss
ON mo.SHOPPER_ID = ss.SHOPPER_ID
INNER JOIN Order oo
ON mo.SHOPPER_ID = oo.SHOPPER_ID AND mo.DATE = oo.DATE

以下是SQL Fiddle试用

Answer 4

SELECT *
FROM
Shopper s
CROSS APPLY
(
SELECT TOP 1 *
FROM
Order o
WHERE
s.SHOPPER_ID = o.SHOPPER_ID
ORDER BY
o.DATE DESC
) o;

Answer 5

Select s.*, o1.* 
From Order as o1
left join Order as o2
on (o1.SHOPPER_ID = o2.SHOPPER_ID and o1.DATE < o2.DATE)
join Shopper as s
on (s.SHOPPER_ID = o1.SHOPPER_ID )
where o2.DATE is NULL;

将Order表连接到自身，寻找更新的订单加入。 “左”连接意味着Order表中的每一行都将保留在结果中，即使它无法加入该客户的较新订单。

“where”会丢弃找到较新订单的所有行。这使您只能使用最新的订单。

将这些结果加入Shopper表以包含购物者数据。

编辑：我建议这个答案，因为数据库的JOIN比子选择快得多。

一对多加入group by

5 个答案: