sql server 合并多个数据集不重复数据

Question

给定三个表 Ta、Tb、Tc：

Ta(ID, Field1)
Tb(ID, Field2)
Tc(ID, Field3)

给定数据示例：

Ta
ID Field1
---------
1  A
1  B

Tb
ID Field2
---------
1  C
1  D
2  E

Tc
ID Field3
---------
1  F
2  G
2  H

问题： 如何加入这些数据以返回：

ID Field1 Field2 Field3
-----------------------
1  A      C      F
1  B      D      NULL
2  NULL   E      G
2  NULL   NULL   H

我认为我可以通过外部连接来实现这一点，但似乎并非如此。分组的顺序并不重要，只要我带回没有重复行的所有信息即可。

只是为了澄清。只要结果集以最少的行数返回所有数据，我并不介意我得到哪种组合。这是我正在尝试做的一个更现实的例子：

给定一个人，叫他约翰。他有两个电话号码和三个电子邮件地址：

PID  Email
---------
John john@test.com
John john@mail.com
John john@john.com

PID  Tel
--------
John 011
John 022

我想回来：

PID  Email         Tel
----------------------
John john@test.com 011
John john@mail.com 022
John john@john.com NULL

Answer 1

您可以通过以下方式接近：

select coalesce(ta.id, tb.id, tc.id), ta.field1, tb.field2, tc.field3
from (select ta.*, row_number() over (partition by id order by (select NULL)) as seqnum
      from ta
     ) ta full outer join
     (select tb.*, row_number() over (partition by id order by (select NULL)) as seqnum
      from tb
     ) tb
     on ta.id = tb.id and
        ta.seqnum = tb.seqnum
     (select tc.*, row_number() over (partition by id order by (select NULL)) as seqnum
      from tc
     ) tc
     on coalesce(ta.id, tb.id) = tc.id and
        coalesce(ta.seqnum, tb.seqnum) = tc.seqnum
group by coalesce(ta.id, tb.id, tc.id),
         coalesce(ta.seqnum, tb.seqnum, tc.seqnum)
order by 1, 2

正如我所说，不过，在我的评论中，不能保证表中行的顺序，因此这些可能不会按照您期望的顺序出现。使用您的示例数据，您可以使用：

over (partition by id order by field<n>)

如果字段定义了排序

Answer 2

这是一种替代方法，使用 CTE 和联合，使用 MIN 排除空值。它不能保证顺序，但既然你说你不在乎，只要 ID 都在场。

SQL 小提琴here

WITH TaRanked AS
(
  SELECT ROW_NUMBER() OVER (PARTITION BY ID ORDER BY Field1) as Rnk, ID, Field1
  FROM Ta
),
TbRanked AS
(
  SELECT ROW_NUMBER() OVER (PARTITION BY ID ORDER BY Field2) as Rnk, ID, Field2
  FROM Tb
),
TcRanked AS
(
  SELECT ROW_NUMBER() OVER (PARTITION BY ID ORDER BY Field3) as Rnk, ID, Field3
  FROM Tc
),
TUnion AS
(
    SELECT Rnk, ID, Field1, NULL AS Field2, NULL AS Field3 
        FROM TaRanked 
    UNION ALL
    SELECT Rnk, ID, NULL, Field2, NULL 
        FROM TbRanked 
    UNION ALL
    SELECT Rnk, ID, NULL, NULL, Field3 
        FROM TcRanked 
)
SELECT ID, MIN(Field1), MIN(Field2), MIN(Field3)
  FROM TUnion
  GROUP BY ID, Rnk
  ORDER BY ID, Rnk

结果是

1   A       C       F
1   B       D       (null)
2   (null)  E       G
2   (null)  (null)  H