Stackoverflow - How to join to tables whose names are stored as values in another table?, Sql Server

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DROP TABLE Table1; -- deal with rextester table1 and table2
DROP TABLE Table2;

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 */
)
GO

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', '1', 0x010203040506
UNION ALL SELECT '9', 'Table2', '3', 0x010203040506
UNION ALL SELECT '10', 'Table2', '3', 0x010203040506
UNION ALL SELECT '11', 'Table2', '4', 0x010203040506
UNION ALL SELECT '12', 'Table2', '5', 0x010203040506
UNION ALL SELECT '13', 'Table2', '5', 0x010203040506
UNION ALL SELECT '14', 'Table2', '5', 0x010203040506

UNION ALL SELECT '15', 'Table3', '1', 0x010203040506
UNION ALL SELECT '16', 'Table3', '1', 0x010203040506
UNION ALL SELECT '17', 'Table3', '1', 0x010203040506
UNION ALL SELECT '18', 'Table3', '3', 0x010203040506
UNION ALL SELECT '19', 'Table3', '3', 0x010203040506
UNION ALL SELECT '20', 'Table3', '3', 0x010203040506
UNION ALL SELECT '21', 'Table3', '4', 0x010203040506

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

EXEC(@SQL)

View schema
Execution time: 0,03 sec, rows selected: 26, rows affected: 36, absolute service time: 0,2 sec

Stackoverflow - How to join to tables whose names are stored as values...