Question

Primary    Secondary
-----------------------------------
UST         MUN
Data        NULL
Tele        Data
Sun         Data
RMDS        Data
Data        NULL
Mor         NULL
UST         NULL
Data        Bridge

我想检查＆＃34; Secondary＆＃34;的价值。已经在＆＃34;主要＆＃34;那应该是＆＃34;主要＆＃34;但如果它不在＆＃34;主要＆＃34;价值必须来自＆＃34;中学＆＃34;仅限列。

我希望输出为：

Primary  Secondary
------  -----------
UST      MUN
Data     Bridge
Tele
Sun
RMDS
Mor
Bridge

Answer 1

是的 - 你做到了！

您已经获得了足够的经验来与SQL中的自联接斗争......这是您职业发展生涯中的一个重要里程碑

请 - 使用下面的文章（这真的很棒）来弄清楚如何将辅助字段链接到您自己加入的主要字段......基本上它是：）

链接：https://blog.sqlauthority.com/2010/07/08/sql-server-the-self-join-inner-join-and-outer-join/

Answer 2

假设在Primary下的Bridge不应出现在OUTPUT中。请在下面找到。

SELECT [primary],ISNULL(MAX([Secondary]),'') as [Secondary]
FROM
(SELECT T1.[primary],T2.[Secondary]
FROM 
(SELECT [primary]
FROM #T) T1
JOIN 
(SELECT [primary],[Secondary]
FROM #T  WHERE [Secondary] NOT IN (SELECT [primary]
FROM #T)) T2
ON T1. [primary] = T2.[primary]
GROUP BY T1.[primary],T2.[Secondary]

UNION 

SELECT ONE,NULL FROM
(SELECT [Primary] AS ONE FROM #T
EXCEPT
SELECT [Secondary] FROM #T) X) M
GROUP BY [Primary]

Answer 3

解决方案的线索是使用Join：

全外连接（连接类型）与您想要的非常接近。

SELECT 
* 
FROM
(select distinct [Primary] from test) t1 
Full outer JOIN
(select distinct Secondary 
from test where Secondary not in (select distinct [Primary] from test)) t2
ON t1.[Primary] = t2.Secondary

<强>结果： -

Primary Secondary
NULL    Bridge
Data    NULL
Mor     NULL
NULL    MUN
RMDS    NULL
Sun     NULL
Tele    NULL
UST     NULL

在同一张表中应用条件

3 个答案: