如何仅返回加入时的最新记录 [英] How to return only latest record on join

问题描述

我正在加入桌子.我只想根据日期字段从联接表中返回一条记录.

I'm joining tables. I only want to return one record from the joining table, based on a date field.

这是到目前为止我所做的简化工作: http://sqlfiddle.com/#！3/be0cdd/2

Here's a simplified fiddle of what I've done so far: http://sqlfiddle.com/#!3/be0cdd/2

我的桌子:

  CUSTOMER

| CustomerID |
--------------
| 1          |


  PURCHASE

| PurchaseID | CustomerID | ProductID | CreateDate | ArchiveFlag |
------------------------------------------------------------------
| 1          | 1          | 443       | 01-FEB-15  | F           |
| 2          | 1          | 551       | 01-MAR-15  | F           |
| 3          | 1          | 151       | 01-JAN-15  | F           |
| 4          | 1          | 654       | 01-MAY-15  | T           |
| 5          | 1          | 345       | 01-APR-15  | T           |

这是查询本身:

select *
from customer c
join purchase p
on c.customerid = p.customerid
and p.archiveflag = 'F';

我只想返回未归档的每个客户的最新购买信息(在此示例中，购买ID为2).

I only want to return the latest purchase that isn't archived (in this example, purchase ID 2) for each customer.

理想的输出:

| CustomerID | PurchaseID | CustomerID_2 | ProductID | CreateDate | ArchiveFlag |
|--------------------------------------------------------------------------------
| 1          | 2          | 1            | 551       | 01-MAR-15  | F           |

推荐答案

Oracle 12c引入了行限制子句，您可以这样做(如果您只想要一个结果):

Oracle 12c introduced a row limiting clause and you could do (if you only want a single result):

SELECT *
FROM   customer c
       INNER JOIN purchase p
       ON ( c.customerid = p.customerid )
WHERE  p.archiveflag = 'F'
ORDER BY
       CreateDate DESC
FETCH FIRST 1 ROW ONLY

在早期版本中，您可以执行以下操作:

In earlier versions you can do:

SQL提琴

Oracle 11g R2架构设置:

create table CUSTOMER(CustomerID INT);
create table PURCHASE(PurchaseID INT, CustomerID INT, ProductID INT, CreateDate date, ArchiveFlag char);

insert into CUSTOMER values(1);
insert into CUSTOMER values(2);

insert into PURCHASE values(1,1,443,'01-FEB-15','F');
insert into PURCHASE values(2,1,551,'01-MAR-15','F');
insert into PURCHASE values(3,1,151,'01-JAN-15','F');
insert into PURCHASE values(4,1,654,'01-MAY-15','T');
insert into PURCHASE values(5,1,345,'01-APR-15','T');
insert into PURCHASE values(6,2,234,'01-MAY-15','T');
insert into PURCHASE values(7,2,134,'01-APR-15','F');
insert into PURCHASE values(8,2,999,'01-JAN-15','F');
insert into PURCHASE values(9,2,724,'07-JUN-15','F');
insert into PURCHASE values(10,2,345,'01-JUN-15','T');

查询1-如果您只想获取单个客户的最新信息:

SELECT *
FROM   (
  SELECT *
  FROM   Purchase
  WHERE  archiveflag = 'F'
  AND    CustomerID = 1
  ORDER BY
         CreateDate DESC
)
WHERE ROWNUM = 1

结果 :

Results:

| PURCHASEID | CUSTOMERID | PRODUCTID |              CREATEDATE | ARCHIVEFLAG |
|------------|------------|-----------|-------------------------|-------------|
|          2 |          1 |       551 | March, 01 2015 00:00:00 |           F |

查询2-如果要获取所有客户的最新信息:

SELECT PurchaseID,
       CustomerID,
       ProductID,
       CreateDate,
       ArchiveFlag
FROM   (
  SELECT p.*,
         ROW_NUMBER() OVER ( PARTITION BY p.CustomerID ORDER BY CreateDate DESC ) RN
  FROM   purchase p
  WHERE  ArchiveFlag = 'F'
)
WHERE  RN = 1

结果 :

Results:

| PURCHASEID | CUSTOMERID | PRODUCTID |              CREATEDATE | ARCHIVEFLAG |
|------------|------------|-----------|-------------------------|-------------|
|          2 |          1 |       551 | March, 01 2015 00:00:00 |           F |
|          9 |          2 |       724 |  June, 07 2015 00:00:00 |           F |

如果 PURCHASE.CUSTOMERID 是链接到 CUSTOMER.CUSTOMERID 的非空外键，则无需连接表(如上所述).

If PURCHASE.CUSTOMERID is a not null foreign key linked to CUSTOMER.CUSTOMERID then you do not need to join the tables (as above).

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