oracle 如何在SQL中删除join中的重复列

ca1c2owp 于 2023-05-28 发布在 Oracle

关注(0)|答案(2)|浏览(233)

我有下面的代码

SELECT *
FROM
    customer
INNER JOIN (
    SELECT
        customerid, newspapername, enddate, n.publishedby
    FROM
        newspapersubscription ns,
        newspaper n
    WHERE
        publishedby IN (
            SELECT publishedby
            FROM newspaper
            WHERE ns.newspapername = n.NewspaperName
        )
    UNION
    SELECT
        customerid, Magazinename, enddate, m.publishedby
    FROM
        magazinesubscription ms,
        magazine m
    WHERE
        publishedby IN (
            SELECT publishedby
            FROM magazine
            WHERE ms.Magazinename = m.MagazineName
        )
) ON
    customer.customerid = customerid
ORDER BY
    customer.customerid;

客户表具有以下内容：

customerid | customername | customersaddress

此查询返回以下结果：

customerid | customername | customersaddress | customerid | newspapername | enddate| publishedby

我真正想要的是

customerid | customername | customersaddress | newspapername | magazinename | enddate| publishedby

这里，如果存在magazinename，newspapername字段应该为空，反之亦然。此外，联合操作中的customerid的重复字段不应该出现，而在我的结果中，newspapername和magazinename的值都放在newspapername title下。
我该怎么做？

oracle

来源：https://stackoverflow.com/questions/36808295/how-to-remove-duplicate-columns-from-join-in-sql

2条答案

按热度按时间

hgqdbh6s1#

由于您使用'*'查询表，因此您将始终获得两个表中的所有列。为了省略此列，您必须手动命名要查询的所有列。为了满足您的其他需求，您只需要在联合查询中的每个子句中插入一个伪列。下面是一个例子，应该工作，以允许你想要的-

SELECT customer.customerid, customer.customername, customer.customeraddress, newspapername, magazinename, enddate, publishedby 
FROM customer
INNER JOIN
(select  customerid, newspapername, null Magazinename, enddate, n.publishedby 
 from newspapersubscription ns, newspaper n 
 where publishedby in(select publishedby 
                    from newspaper 
                    where ns.newspapername = n.NewspaperName)
UNION
select  customerid, null newspapername, Magazinename, enddate, m.publishedby 
from magazinesubscription ms, magazine m 
 where publishedby in(select publishedby 
                    from magazine 
                     where ms.Magazinename = m.MagazineName))
on customer.customerid = customerid
ORDER BY customer.customerid;

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nkoocmlb2#

要获得所需的投影，请构建正确形状的子查询，并将其联合以获得结果集。UNION ALL比UNION好，因为它避免了排序：你知道你会得到一个不同的集合，因为你在两个不同的表上连接。

select * from (
    select customer.* 
           , n.newspapername
           , null as magazinename
           , ns.enddate
          , n.publishedby 
    from customer
        join newspapersubscription ns 
            on ns.customerid = customer.customerid
        join newspaper n
            on  n.newspapername = ns.newspapername 
    union all
    select customer.* 
           , null as newspapername
           , m.magazinename
           , ms.enddate
           , m.publishedby 
    from customer
        join magazinesubscription  ms 
            on ms.customerid = customer.customerid
        join magazine m
            on  m.magazinename = ms.magazinename 
            )
order by customerid, newspapername nulls last, magazinename ;

下面是我的玩具数据集的输出（缺少publishedby列：

CUSTOMERID CUSTOMERNAME         NEWSPAPERNAME          MAGAZINENAME           ENDDATE
---------- -------------------- ---------------------- ---------------------- ---------
        10 DAISY-HEAD MAISIE    THE DAILY BUGLE                               30-SEP-17
        30 FOX-IN-SOCKS         THE DAILY BUGLE                               30-SEP-17
        30 FOX-IN-SOCKS         THE WHOVILLE TIMES                            30-SEP-16
        30 FOX-IN-SOCKS                                GREEN NEWS             31-DEC-17
        30 FOX-IN-SOCKS                                TWEETLE BEETLE MONTHLY 31-DEC-16
        40 THE LORAX                                   GREEN NEWS             31-DEC-18

6 rows selected.

SQL>

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oracle 如何在SQL中删除join中的重复列

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