如何加入名称作为值存储在另一个 table 中的 table？

Question

Ι 有一些 tables（例如 [Table1]、[Table2]、[Table3] 等等），其中 [ID] 作为主键和RecTime 每个 DATETIME。

我也有一个 table [Files] 将文件保存在 varbinary(max) 列中，并引用其他 table 具有它们的名称和 ID。

[Table2]、[Table3] 和其他结构不同，但共享 [ID] 和 [RecTime] 列与 [Table1]

完全相同

下面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

如何将 [Files] table 连接到其他 table，其中的 Name 和 ID 派生自“[文件”中的值]' table ？

我需要 [Files] table 中的 [BinaryData] 和 [Files] table 中相应 table 参考中的 [RecTime]。

真正的问题是 [Table1]、[Table2] 和 [Table3] 并不是唯一被引用的 tables [Files] table。可以创建新的 tables，其二进制数据必须存储在 [Files] table.

所以我正在寻找一种动态 "join" 它们的方法。

P.S。我不是这个系统的创造者，无法对其进行任何结构上的改变，只是想解决这个问题。

如有任何帮助，我们将不胜感激。

Answer 1

试试下面的方法。

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

Answer 2

一个解决方案是对 @Files table 中的每一行使用 cursor that executes some dynamic 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;

在线演示： http://rextester.com/DXCK86463

Answer 3

这是执行上述操作的最简单的方法。不需要 looping 或任何东西。您需要动态代码，因为可以随时添加表格。

注意： 在 Files table 的示例数据中 tblId 似乎有错误的数据？

所以我正在更改您的数据以将 ID 与相应的 table 相匹配。

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

现在你的动态查询部分：

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)

如果您想查看 @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'

*/

Answer 4

这种设计只是一种在 ER 中建模层次结构的方法。您基本上有一个基于 table 名称（即 Table1、Table2 等）的物理分区 table。因此，加入这些 table 的最简单方法是创建一个 分区视图 然后加入它。

对于您的示例，您只需要做：

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

现在只需像往常一样将它与 Files table 连接起来（记得也要指定分区字段）：

例如这个：

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

给出预期结果：

注意一件重要的事情：因为它是分区视图 SQL 服务器能够执行 分区消除 从而大大加快连接速度（这里的正确术语应该是table消除)。

比如之前的执行计划是：

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'

我们将得到这个执行计划（注意根本没有扫描两个 table）：

当然，为了使用分区视图，您必须首先能够创建它。您可以使用如下查询以编程方式查找特定字段：

;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;

Answer 5

一种方法是创建一个将包含所有表数据的 cte（当然，使用动态 sql 来创建它），然后 select 从剩余的文件中加入该 cte。

这样，动态sql的编写和维护都非常简单，而且它产生的sql it 语句也非常简单：

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)'

你从这里得到的 sql 状态是：

;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)

要执行它：

EXEC(@SQL)

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

Answer 6

如果你只有几个表，那么你可以这样做，它可能会稍微快一些，因为它避免了动态 SQL。

如果您不知道会有多少张桌子或者是否太多，请看这里的其他解决方案（我喜欢 Steve chamber 的解决方案）。

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

演示：http://rextester.com/FWWD90002

Answer 7

查看以下链接。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

如何加入名称作为值存储在另一个 table 中的 table？

How to join to tables whose names are stored as values in another table?

sql

sql-server

sql-server-2012

dynamic-sql

cursors