如何连接到名称在另一个表中存储为值的表？

Ι have some tables ( eg. [Table1], [Table2], [Table3] and so on ) with a [ID] as primary key and a RecTime as DATETIME on each.

Ι有一些表（例如[表1]，[表2]，[表3]等），其中[ID]作为主键，RecTime作为DATETIME。

Αlso Ι have a table [Files] that hold files in a varbinary(max) column, and refers to the other tables having their Names and IDs.

ΑlsoΙ有一个表[Files]，用于保存varbinary（max）列中的文件，并引用具有其Names和ID的其他表。

[Table2], [Table3] and others have different structure, but share the [ID] and [RecTime] column exactly as in [Table1]

[表2]，[表3]等具有不同的结构，但与[表1]中的[ID]和[RecTime]列完全相同

Below is a quick sample to visualize data.

以下是可视化数据的快速示例。

DECLARE @Table1 as table (
      [ID] [bigint]
    , [RecTime] [datetime]
)
DECLARE @Table2 as table (
      [ID] [bigint]
    , [RecTime] [datetime]
)
DECLARE @Table3 as table (
      [ID] [bigint]
    , [RecTime] [datetime]
)

DECLARE @Files as table (
      [ID] [bigint]
    , [tblName] nvarchar(255) NULL
    , [tblID] bigint NULL
    , [BinaryData]  varbinary(max)
    /* and some other columns */
)

INSERT INTO @Table1 (
      [ID]
    , [RecTime]
)
          SELECT '1', DATEADD(day, (ABS(CHECKSUM(NEWID())) % 65530), 0)
UNION ALL SELECT '2', DATEADD(day, (ABS(CHECKSUM(NEWID())) % 65530), 0)
UNION ALL SELECT '3', DATEADD(day, (ABS(CHECKSUM(NEWID())) % 65530), 0)
UNION ALL SELECT '4', DATEADD(day, (ABS(CHECKSUM(NEWID())) % 65530), 0)
UNION ALL SELECT '5', DATEADD(day, (ABS(CHECKSUM(NEWID())) % 65530), 0)

INSERT INTO @Table2 (
      [ID]
    , [RecTime]
)
          SELECT '11', DATEADD(day, (ABS(CHECKSUM(NEWID())) % 65530), 0)
UNION ALL SELECT '12', DATEADD(day, (ABS(CHECKSUM(NEWID())) % 65530), 0)
UNION ALL SELECT '13', DATEADD(day, (ABS(CHECKSUM(NEWID())) % 65530), 0)
UNION ALL SELECT '14', DATEADD(day, (ABS(CHECKSUM(NEWID())) % 65530), 0)
UNION ALL SELECT '15', DATEADD(day, (ABS(CHECKSUM(NEWID())) % 65530), 0)

INSERT INTO @Table3 (
      [ID]
    , [RecTime]
)
          SELECT '21', DATEADD(day, (ABS(CHECKSUM(NEWID())) % 65530), 0)
UNION ALL SELECT '22', DATEADD(day, (ABS(CHECKSUM(NEWID())) % 65530), 0)
UNION ALL SELECT '23', DATEADD(day, (ABS(CHECKSUM(NEWID())) % 65530), 0)
UNION ALL SELECT '24', DATEADD(day, (ABS(CHECKSUM(NEWID())) % 65530), 0)
UNION ALL SELECT '25', DATEADD(day, (ABS(CHECKSUM(NEWID())) % 65530), 0)

INSERT INTO @Files (
      [ID]
    , [tblName]
    , [tblID]
    , [BinaryData]
)
          SELECT '1', 'Table1', '1', 0x010203040506
UNION ALL SELECT '2', 'Table1', '2', 0x010203040506
UNION ALL SELECT '3', 'Table1', '2', 0x010203040506
UNION ALL SELECT '4', 'Table1', '3', 0x010203040506
UNION ALL SELECT '5', 'Table1', '4', 0x010203040506
UNION ALL SELECT '6', 'Table1', '5', 0x010203040506
UNION ALL SELECT '7', 'Table1', '5', 0x010203040506

UNION ALL SELECT '8', 'Table2', '11', 0x010203040506
UNION ALL SELECT '9', 'Table2', '11', 0x010203040506
UNION ALL SELECT '10', 'Table2', '12', 0x010203040506
UNION ALL SELECT '11', 'Table2', '13', 0x010203040506
UNION ALL SELECT '12', 'Table2', '14', 0x010203040506
UNION ALL SELECT '13', 'Table2', '12', 0x010203040506
UNION ALL SELECT '14', 'Table2', '15', 0x010203040506

UNION ALL SELECT '15', 'Table3', '21', 0x010203040506
UNION ALL SELECT '16', 'Table3', '22', 0x010203040506
UNION ALL SELECT '17', 'Table3', '24', 0x010203040506
UNION ALL SELECT '18', 'Table3', '23', 0x010203040506
UNION ALL SELECT '19', 'Table3', '25', 0x010203040506
UNION ALL SELECT '20', 'Table3', '25', 0x010203040506
UNION ALL SELECT '21', 'Table3', '21', 0x010203040506

SELECT * FROM @Table1
SELECT * FROM @Table2
SELECT * FROM @Table3

SELECT * FROM @Files

How can I join [Files] table to other tables, the Name and ID of which derive from a value in '[Files]' table ?

如何将[Files]表连接到其他表，其名称和ID派生自'[Files]'表中的值？

I need [BinaryData] from [Files] table and [RecTime] from respective table reference in [Files] table.

我需要[Files]表中的[BinaryData]和[Files]表中各个表引用的[RecTime]。

The real problem is that [Table1], [Table2] and [Table3] are not the only tables that are referred [Files] table. New tables can be created, for which binary data must be stored in [Files] table.

真正的问题是[Table1]，[Table2]和[Table3]不是唯一被称为[Files]表的表。可以创建新表，二进制数据必须存储在[Files]表中。

So I'm looking for a way to "join" them dynamically.

所以我正在寻找一种动态“加入”它们的方法。

P.S. I'm not the creator of this system, and can not perform any structural change on it, but just trying to solve this problem.

附：我不是这个系统的创造者，不能对它进行任何结构改变，而只是试图解决这个问题。

Any help would be appreciated.

任何帮助，将不胜感激。

7 个解决方案

#1

This is the simplest way to do the above. No need of looping or any thing. You need dynamic code as Tables can be add at any time.

这是完成上述操作的最简单方法。不需要循环或任何事情。您需要动态代码，因为可以随时添加表。

Note: In your sample data for Files table seems have wrong data in tblId ?

注意：在你的示例数据中，Files表似乎在tblId中有错误的数据？

So I am changing your data to match IDs to respective tables.

所以我正在更改您的数据以匹配各个表的ID。

Schema:

架构：

CREATE TABLE Table1   (
      [ID] [bigint]
    , [RecTime] [datetime]
)
CREATE TABLE Table2 (
      [ID] [bigint]
    , [RecTime] [datetime]
)
CREATE TABLE Table3 (
      [ID] [bigint]
    , [RecTime] [datetime]
)

CREATE TABLE Files (
      [ID] [bigint]
    , [tblName] nvarchar(255) NULL
    , [tblID] bigint NULL
    , [BinaryData]  varbinary(max)
    /* and some other columns */
)

INSERT INTO Table1 (
      [ID]
    , [RecTime]
)
          SELECT '1', DATEADD(day, (ABS(CHECKSUM(NEWID())) % 65530), 0)
UNION ALL SELECT '2', DATEADD(day, (ABS(CHECKSUM(NEWID())) % 65530), 0)
UNION ALL SELECT '3', DATEADD(day, (ABS(CHECKSUM(NEWID())) % 65530), 0)
UNION ALL SELECT '4', DATEADD(day, (ABS(CHECKSUM(NEWID())) % 65530), 0)
UNION ALL SELECT '5', DATEADD(day, (ABS(CHECKSUM(NEWID())) % 65530), 0)

INSERT INTO Table2 (
      [ID]
    , [RecTime]
)
          SELECT '11', DATEADD(day, (ABS(CHECKSUM(NEWID())) % 65530), 0)
UNION ALL SELECT '12', DATEADD(day, (ABS(CHECKSUM(NEWID())) % 65530), 0)
UNION ALL SELECT '13', DATEADD(day, (ABS(CHECKSUM(NEWID())) % 65530), 0)
UNION ALL SELECT '14', DATEADD(day, (ABS(CHECKSUM(NEWID())) % 65530), 0)
UNION ALL SELECT '15', DATEADD(day, (ABS(CHECKSUM(NEWID())) % 65530), 0)

INSERT INTO Table3 (
      [ID]
    , [RecTime]
)
          SELECT '21', DATEADD(day, (ABS(CHECKSUM(NEWID())) % 65530), 0)
UNION ALL SELECT '22', DATEADD(day, (ABS(CHECKSUM(NEWID())) % 65530), 0)
UNION ALL SELECT '23', DATEADD(day, (ABS(CHECKSUM(NEWID())) % 65530), 0)
UNION ALL SELECT '24', DATEADD(day, (ABS(CHECKSUM(NEWID())) % 65530), 0)
UNION ALL SELECT '25', DATEADD(day, (ABS(CHECKSUM(NEWID())) % 65530), 0)

INSERT INTO Files (
      [ID]
    , [tblName]
    , [tblID]
    , [BinaryData]
)
          SELECT '1', 'Table1', '1', 0x010203040506
UNION ALL SELECT '2', 'Table1', '2', 0x010203040506
UNION ALL SELECT '3', 'Table1', '2', 0x010203040506
UNION ALL SELECT '4', 'Table1', '3', 0x010203040506
UNION ALL SELECT '5', 'Table1', '4', 0x010203040506
UNION ALL SELECT '6', 'Table1', '5', 0x010203040506
UNION ALL SELECT '7', 'Table1', '5', 0x010203040506

UNION ALL SELECT '8', 'Table2', '11', 0x010203040506
UNION ALL SELECT '9', 'Table2', '11', 0x010203040506
UNION ALL SELECT '10', 'Table2', '12', 0x010203040506
UNION ALL SELECT '11', 'Table2', '13', 0x010203040506
UNION ALL SELECT '12', 'Table2', '14', 0x010203040506
UNION ALL SELECT '13', 'Table2', '12', 0x010203040506
UNION ALL SELECT '14', 'Table2', '15', 0x010203040506

UNION ALL SELECT '15', 'Table3', '21', 0x010203040506
UNION ALL SELECT '16', 'Table3', '22', 0x010203040506
UNION ALL SELECT '17', 'Table3', '24', 0x010203040506
UNION ALL SELECT '18', 'Table3', '23', 0x010203040506
UNION ALL SELECT '19', 'Table3', '25', 0x010203040506
UNION ALL SELECT '20', 'Table3', '25', 0x010203040506
UNION ALL SELECT '21', 'Table3', '21', 0x010203040506

Now your Dynamic Query Part:

现在您的动态查询部分：

DECLARE @QRY VARCHAR(MAX)='', @Tables VARCHAR(MAX)='';

--Capturing List of Table names for selecting RecTime
SELECT @Tables = @Tables+ tblName+'.RecTime,' FROM (
SELECT DISTINCT tblName FROM Files
)A

--To remove last comma
SELECT @Tables = SUBSTRING(@Tables,1, LEN(@Tables)-1)

--Preparing Dynamic Qry
SELECT @QRY = '
SELECT Files.ID,Files.BinaryData
,COALESCE('+@Tables+') AS RecTime
FROM Files '

SELECT @QRY =@QRY+ JOINS FROM (
SELECT  DISTINCT '
LEFT JOIN '+ tblName + ' ON Files.tblID = '+tblName+'.ID AND Files.tblName= '''+tblName+''''
as JOINS
FROM Files
)A

print @QRY

EXEC( @QRY)

If you want to see what @Qry contains

如果你想看看@Qry包含的内容

/*
Print Output:

SELECT Files.ID,Files.BinaryData
,COALESCE(Table1.RecTime,Table2.RecTime,Table3.RecTime) AS RecTime
FROM Files 
LEFT JOIN Table1 ON Files.tblID = Table1.ID AND Files.tblName= 'Table1'
LEFT JOIN Table2 ON Files.tblID = Table2.ID AND Files.tblName= 'Table2'
LEFT JOIN Table3 ON Files.tblID = Table3.ID AND Files.tblName= 'Table3'

*/

#2

One approach is to create a cte that will contain all the tables data (of course, using dynamic sql to create it), and then select from files left join that cte.

一种方法是创建一个包含所有表数据的cte（当然，使用动态sql创建它），然后从文件中选择左连接cte。

This way, the dynamic sql is quite simple to write and maintain, and also the sql it statement it produces is very simple:

这样，动态sql的编写和维护非常简单，而且它生成的sql语句非常简单：

DECLARE @SQL varchar(max) = ''
SELECT @SQL = @SQL +' UNION ALL SELECT ID, 
                                       RecTime, 
                                       '''+ tblName +''' AS TableName 
                                FROM ' + tblName 
FROM (
    SELECT DISTINCT tblName FROM files    
) x
-- replace the first 'UNION ALL' with ';WITH allTables as ('
SELECT @SQL = STUFF(@SQL, 1, 11, ';WITH allTables as (') 
       +') 
       SELECT * 
       FROM Files 
       LEFT JOIN allTables ON(tblName = TableName AND tblId = allTables.Id)'

The sql statemet you get from this is:

你从中获得的sql statemet是：

;WITH allTables as ( 
    SELECT ID, RecTime, 'Table1' AS TableName 
    FROM Table1 
    UNION ALL  
    SELECT ID, RecTime, 'Table2' AS TableName 
    FROM Table2 
    UNION ALL  
    SELECT ID, RecTime, 'Table3' AS TableName 
    FROM Table3
 ) 
 SELECT * 
 FROM Files 
 LEFT JOIN allTables ON(tblName = TableName AND tblId = allTables.Id)

To execute it:

执行它：

EXEC(@SQL)

Results:

结果：

ID    tblName   tblID   BinaryData  ID    RecTime                 TableName
1     Table1    1       123456      1       31.03.2060 00:00:00   Table1
2     Table1    2       123456      2       03.12.1997 00:00:00   Table1
3     Table1    2       123456      2       03.12.1997 00:00:00   Table1
4     Table1    3       123456      3       02.07.2039 00:00:00   Table1
5     Table1    4       123456      4       17.06.1973 00:00:00   Table1
6     Table1    5       123456      5       06.12.2076 00:00:00   Table1
7     Table1    5       123456      5       06.12.2076 00:00:00   Table1
8     Table2    1       123456      NULL    NULL                    NULL
9     Table2    3       123456      NULL    NULL                    NULL
10    Table2    3       123456      NULL    NULL                    NULL
11    Table2    4       123456      NULL    NULL                    NULL
12    Table2    5       123456      NULL    NULL                    NULL
13    Table2    5       123456      NULL    NULL                    NULL
14    Table2    5       123456      NULL    NULL                    NULL
15    Table3    1       123456      NULL    NULL                    NULL
16    Table3    1       123456      NULL    NULL                    NULL
17    Table3    1       123456      NULL    NULL                    NULL
18    Table3    3       123456      NULL    NULL                    NULL
19    Table3    3       123456      NULL    NULL                    NULL
20    Table3    3       123456      NULL    NULL                    NULL
21    Table3    4       123456      NULL    NULL                    NULL

Live demo on rextester

rextester上的现场演示

#3

One solution is to use a cursor that executes some dynamic SQL for each row in the @Files table:

一种解决方案是使用游标为@Files表中的每一行执行一些动态SQL：

-- Copy table variables into temporary tables so they can be referenced from dynamic SQL
SELECT * INTO #Table1 FROM @Table1;
SELECT * INTO #Table2 FROM @Table2;
SELECT * INTO #Table3 FROM @Table3;

-- Create a temporary table for storing the results
CREATE TABLE #results (
      [ID] [bigint]
    , [tblName] nvarchar(255) NULL
    , [tblID] bigint NULL
    , [BinaryData]  varbinary(max)
    , [RecTime] [datetime]
);

-- Declare placeholders and cursor
DECLARE @ID bigint;
DECLARE @tblName nvarchar(255);
DECLARE @tblID bigint;
DECLARE @BinaryData varbinary(max);
DECLARE @RecTime datetime;
DECLARE @sql nvarchar(max);
DECLARE @params nvarchar(max);

DECLARE files_cursor CURSOR FOR  
SELECT ID, tblName, tblID, BinaryData
FROM @Files

-- Loop over all rows in the @Files table
OPEN files_cursor   
FETCH NEXT FROM files_cursor INTO @ID, @tblName, @tblID, @BinaryData

WHILE @@FETCH_STATUS = 0   
BEGIN   
   -- Find the referenced table row and extract its RecTime.
   SET @RecTime = NULL;
   SET @sql = CONCAT(
       'SELECT @RecTime = RecTime FROM #', @tblName, ' WHERE ID = ', @tblID);
   SET @params = '@RecTime datetime out';

   EXEC SP_EXECUTESQL @sql, @params, @RecTime out;

   -- Add result
   INSERT INTO #results (ID, tblName, tblID, BinaryData, RecTime)
   VALUES (@ID, @tblName, @tblID, @BinaryData, @RecTime); 

   FETCH NEXT FROM files_cursor INTO @ID, @tblName, @tblID, @BinaryData;
END   

-- Finalise
CLOSE files_cursor;
DEALLOCATE files_cursor;

-- Display the results from temporary table
SELECT * FROM #results;

Online demo: http://rextester.com/DXCK86463

在线演示：http：//rextester.com/DXCK86463

#4

This design is just a way to model a hierarchy in ER. You basically have a physically partitioned table based on table names (ie Table1, Table2 and so on). As such the easiest way to join these tables is to create a partitioned view and then join it.

此设计只是在ER中建模层次结构的一种方法。您基本上有一个基于表名的物理分区表（即Table1，Table2等）。因此，连接这些表的最简单方法是创建分区视图然后加入它。

In the case of your example you just have to do:

在您的示例中，您只需要执行以下操作：

CREATE VIEW vmAll AS
SELECT 'Table1' AS 'tblName', [ID], [RecTime] FROM Table1
UNION ALL
SELECT 'Table2' AS 'tblName', [ID], [RecTime] FROM Table2
UNION ALL
SELECT 'Table3' AS 'tblName', [ID], [RecTime] FROM Table3;
GO

Now just join it with the Files table as usual (remember to specify the partitioning field too):

现在像往常一样将它与Files表连接（请记住也指定分区字段）：

For example this:

例如：

SELECT 
      F.[ID] 
    , F.[tblName]
    , F.[tblID]
    , F.[BinaryData] 
    , A.RecTime
    FROM [Files] F
LEFT OUTER JOIN vmAll A ON
    F.[ID] = A.[ID] AND
    F.tblName = A.tblName

Gives the expected result:

给出预期结果：

Notice an important thing: since it's a partitioned view SQL Server is able to perform partition elimination thus speeding up the join considerably (the correct term here should be table elimination).

注意一件重要的事情：因为它是一个分区视图，SQL Server能够执行分区消除，从而大大加快了连接速度（这里的正确术语应该是表消除）。

For example the previous execution plan was:

例如，之前的执行计划是：

If we add a filter predicate on the partitioning column:

如果我们在分区列上添加过滤谓词：

SELECT 
      F.[ID] 
    , F.[tblName]
    , F.[tblID]
    , F.[BinaryData] 
    , A.RecTime
    FROM [Files] F
LEFT OUTER JOIN vmAll A ON
    F.[ID] = A.[ID] AND
    F.tblName = A.tblName

WHERE A.tblName = 'Table1'

We will get this execution plan (notice two tables are not scanned at all):

我们将得到这个执行计划（注意根本不扫描两个表）：

Of course in order to use the partitioned view you have to be able to create it first. You can do it programmatically looking for the specific fields with a query like this one:

当然，为了使用分区视图，您必须首先创建它。您可以通过编程方式查找具有以下查询的特定字段：

;WITH CTE AS
(
    SELECT C.object_id FROM sys.columns C
    INNER JOIN sys.objects O ON C.object_id = O.object_id
    WHERE 
        (C.[name] = 'ID' OR C.[name] = 'RecTime')
        AND O.[type] = 'U'
    GROUP BY C.object_id
    HAVING COUNT(*) = 2
)
SELECT OBJECT_NAME(object_id), object_id FROM CTE;

#5

Try the following.

请尝试以下方法。

Select res.* , F.* From Files F
Left join
(
Select 'table1' as tablename, a.* From table1 a
Union
Select 'table2' as tablename, b.* From table2 b
Union
Select 'table3' as tablename, c.* From table3 c
)Res
On res.tablename = F.tblname

#6

Have a look on below links. this might solve your problem.

看看下面的链接。这可能会解决您的问题。

MySQL join tables where table name is a field of another table , MySQL join tables where table name is a field of another table

MySQL连接表，其中表名是另一个表的字段，MySQL连接表，其中表名是另一个表的字段

#7

If you have only few tables, then you can just do this, It could be slightly faster because it avoids Dynamic SQL.

如果您只有几个表，那么您可以这样做，它可能会稍快一些，因为它可以避免动态SQL。

Look at other solutions(I like Steve chamber's solution) here if you can't tell how many tables there will be or if there will be too many.

看看其他解决方案（我喜欢史蒂夫室的解决方案），如果你不知道将会有多少表或者会有太多表。

SELECT F.*, RecTime = 
      CASE tblName  
         WHEN 'Table1' THEN COALESCE(T1.RecTime, NULL)
         WHEN 'Table2' THEN COALESCE(T2.RecTime, NULL)
         WHEN 'Table3' THEN COALESCE(T3.RecTime, NULL)
         ELSE NULL
      END 
FROM @Files F
LEFT JOIN @Table1 T1 ON F.tblID = T1.ID
LEFT JOIN @Table2 T2 ON F.tblID = T2.ID
LEFT JOIN @Table3 T3 ON F.tblID = T3.ID

Demo : http://rextester.com/FWWD90002

演示：http：//rextester.com/FWWD90002

#1