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:
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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