SQL Server从多个表中选择列名

我在SQL Server中有三个表，其结构如下：

col1 col2 a1 a2。。。一 col1 col2 b1 b2。。。bn， col1 col2 c1 c2。。。cn

前两个记录是相同的，col1和col2，但是表的长度不同

我需要选择表的列名，我试图实现的结果如下：

col1，col2，a1，b1，c1，a2，b2，c2

---

有办法吗？

这是可能的，但结果被合并到一列三个表中

比如说

SELECT A.col1 +'/' +B.col1 +'/' + C.col1  As Col1 ,
A.col2 +'/' +B.col2 +'/' + C.col2 As col2 ,a1, b1, c1, a2, b2, c2 ,
* FROM A
INNER JOIN B
ON A.ID =B.ID
INNER JOIN C 
ON C.ID = B.ID

---

SQL Server不是创建通用结果集的正确工具。引擎需要提前知道会发生什么。嗯，您可以尝试使用动态SQL找到解决方案

我想提出两种不同的方法

这两种方法都可以处理任意数量的表，只要它们都具有具有适当类型的col1和col2列

让我们先创建一个简单的mokcup场景：

非常务实的方法： 尝试以下简单的完全外部联接：

结果

+------+------+-----------+-----------+------+------+------------+-------------------------+
| col1 | col2 | SomeMore1 | SomeMore2 | col1 | col2 | OtherType1 | OtherType2              |
+------+------+-----------+-----------+------+------+------------+-------------------------+
| 1    | 1    | blah 1.1  | blub 1.1  | 1    | 1    | 101        | 2019-03-08 10:53:20.257 |
+------+------+-----------+-----------+------+------+------------+-------------------------+
| 1    | 2    | blah 1.2  | blub 1.2  | 1    | 2    | 102        | 2019-03-09 10:53:20.257 |
+------+------+-----------+-----------+------+------+------------+-------------------------+
| 1    | 100  | not in t2 | not in t2 | NULL | NULL | NULL       | NULL                    |
+------+------+-----------+-----------+------+------+------------+-------------------------+
| NULL | NULL | NULL      | NULL      | 1    | 200  | 200        | 2019-09-24 10:53:20.257 |
+------+------+-----------+-----------+------+------+------------+-------------------------+

+------+------+-----------------------------------------------------------------------------------------------------------+-----------------------------------------------------------------------------------------------------------------------+
| col1 | col2 | Content1                                                                                                  | Content2                                                                                                              |
+------+------+-----------------------------------------------------------------------------------------------------------+-----------------------------------------------------------------------------------------------------------------------+
| 1    | 1    | <row><col1>1</col1><col2>1</col2><SomeMore1>blah 1.1</SomeMore1><SomeMore2>blub 1.1</SomeMore2></row>     | <row><col1>1</col1><col2>1</col2><OtherType1>101</OtherType1><OtherType2>2019-03-08T11:03:49.877</OtherType2></row>   |
+------+------+-----------------------------------------------------------------------------------------------------------+-----------------------------------------------------------------------------------------------------------------------+
| 1    | 2    | <row><col1>1</col1><col2>2</col2><SomeMore1>blah 1.2</SomeMore1><SomeMore2>blub 1.2</SomeMore2></row>     | <row><col1>1</col1><col2>2</col2><OtherType1>102</OtherType1><OtherType2>2019-03-09T11:03:49.877</OtherType2></row>   |
+------+------+-----------------------------------------------------------------------------------------------------------+-----------------------------------------------------------------------------------------------------------------------+
| 1    | 100  | <row><col1>1</col1><col2>100</col2><SomeMore1>not in t2</SomeMore1><SomeMore2>not in t2</SomeMore2></row> | NULL                                                                                                                  |
+------+------+-----------------------------------------------------------------------------------------------------------+-----------------------------------------------------------------------------------------------------------------------+
| 1    | 200  | NULL                                                                                                      | <row><col1>1</col1><col2>200</col2><OtherType1>200</OtherType1><OtherType2>2019-09-24T11:03:49.877</OtherType2></row> |
+------+------+-----------------------------------------------------------------------------------------------------------+-----------------------------------------------------------------------------------------------------------------------+

但您必须处理非唯一的列名。。。此时，动态创建的语句可以提供帮助

使用容器类型XML的通用方法 当您事先不知道结果时，可以将结果打包到容器中。这允许RDBMS有一个清晰的结构，并将如何处理此集合的问题转移给消费者

cte将读取所有现有的col1和col2对 这对值的每个表行都作为XML插入 任何表中不存在的对显示为NULL 试试这个

WITH AllDistinctCol1Col2Values AS
(
    SELECT col1,col2 FROM @mockup1
    UNION ALL 
    SELECT col1,col2 FROM @mockup2
    --add all your tables here
)
SELECT col1,col2
     ,(SELECT * FROM @mockup1 x WHERE c1c2.col1=x.col1 AND c1c2.col2=x.col2 FOR XML PATH('row'),TYPE) AS Content1 
     ,(SELECT * FROM @mockup2 x WHERE c1c2.col1=x.col1 AND c1c2.col2=x.col2 FOR XML PATH('row'),TYPE) AS Content2
FROM AllDistinctCol1Col2Values c1c2
GROUP BY col1,col2;

结果

+------+------+-----------+-----------+------+------+------------+-------------------------+
| col1 | col2 | SomeMore1 | SomeMore2 | col1 | col2 | OtherType1 | OtherType2              |
+------+------+-----------+-----------+------+------+------------+-------------------------+
| 1    | 1    | blah 1.1  | blub 1.1  | 1    | 1    | 101        | 2019-03-08 10:53:20.257 |
+------+------+-----------+-----------+------+------+------------+-------------------------+
| 1    | 2    | blah 1.2  | blub 1.2  | 1    | 2    | 102        | 2019-03-09 10:53:20.257 |
+------+------+-----------+-----------+------+------+------------+-------------------------+
| 1    | 100  | not in t2 | not in t2 | NULL | NULL | NULL       | NULL                    |
+------+------+-----------+-----------+------+------+------------+-------------------------+
| NULL | NULL | NULL      | NULL      | 1    | 200  | 200        | 2019-09-24 10:53:20.257 |
+------+------+-----------+-----------+------+------+------------+-------------------------+

+------+------+-----------------------------------------------------------------------------------------------------------+-----------------------------------------------------------------------------------------------------------------------+
| col1 | col2 | Content1                                                                                                  | Content2                                                                                                              |
+------+------+-----------------------------------------------------------------------------------------------------------+-----------------------------------------------------------------------------------------------------------------------+
| 1    | 1    | <row><col1>1</col1><col2>1</col2><SomeMore1>blah 1.1</SomeMore1><SomeMore2>blub 1.1</SomeMore2></row>     | <row><col1>1</col1><col2>1</col2><OtherType1>101</OtherType1><OtherType2>2019-03-08T11:03:49.877</OtherType2></row>   |
+------+------+-----------------------------------------------------------------------------------------------------------+-----------------------------------------------------------------------------------------------------------------------+
| 1    | 2    | <row><col1>1</col1><col2>2</col2><SomeMore1>blah 1.2</SomeMore1><SomeMore2>blub 1.2</SomeMore2></row>     | <row><col1>1</col1><col2>2</col2><OtherType1>102</OtherType1><OtherType2>2019-03-09T11:03:49.877</OtherType2></row>   |
+------+------+-----------------------------------------------------------------------------------------------------------+-----------------------------------------------------------------------------------------------------------------------+
| 1    | 100  | <row><col1>1</col1><col2>100</col2><SomeMore1>not in t2</SomeMore1><SomeMore2>not in t2</SomeMore2></row> | NULL                                                                                                                  |
+------+------+-----------------------------------------------------------------------------------------------------------+-----------------------------------------------------------------------------------------------------------------------+
| 1    | 200  | NULL                                                                                                      | <row><col1>1</col1><col2>200</col2><OtherType1>200</OtherType1><OtherType2>2019-09-24T11:03:49.877</OtherType2></row> |
+------+------+-----------------------------------------------------------------------------------------------------------+-----------------------------------------------------------------------------------------------------------------------+

---

这是不可能的，事实上，这是一个毫无意义的问题，除非你也告诉我们这三个表之间的关系。你说一个表有不同的长度是什么意思？实际样本数据和预期结果可能有助于我们了解您在这里追求的目标，但是，目前还不清楚。三个表中的col1和col2是相同的。表1:col1，col2，a1，a2，a3。。。an，表2:col1，col2，b1，b2，b3。。。bn，表3:col1，col2，c1，c2，c3。。。cn我需要选择列标题并实现如下结果：col1、col2、a1、b1、c1、a2、b2、c2、a3、b3、c3等等。很抱歉，我没有SQL Server方面的经验。您有3个表，但不告诉我们如何加入这些表。理想情况下，您可以提供用于创建这些表的实际SQL代码，并指定这些表如何连接以获得所需的输出。