Join table where table name is a value in another table - sql-server

Question

I have been tasked with getting some data out of another database not designed by me, so the design cannot be altered.
Looking at the data I need to join a table dynamically based on the value held in another table.
E.G
SELECT * FROM TableA LEFT JOIN TableB oN TableA.TBID = TableB.ID LEFT JOIN TableB.TableOffset AS C ON C.TableAID = TableA.ID
So table B has a column called TableOffset, this holds the name of the table that needs to be joined on as C
(I've tried to do an SQLFIDDLE but the site isn't working with SQL Server ATM)
The issue is there are 112 attribute tables where the data could be, so doing a left join for every one of them would slow down the query I imagine.
So based on the below I would need to get a result set of:
| TableAID | TableATitle | AttrTableA21 | AttrTableA22 |
|----------|-------------|--------------|--------------|
|1 |test | Name | 2019 |
|2 |test2 | Name 2 | 2016 |
Example SQL Code
CREATE TABLE [dbo].[TableA](
[ID] [int] NOT NULL,
[Title] [nvarchar](100) NOT NULL,
[TableBID] [int] NOT NULL
);
CREATE TABLE [dbo].[TableB](
[ID] [int] NOT NULL,
[TableName] [nvarchar](100) NOT NULL
);
CREATE TABLE [dbo].[ATTR_A](
[ID] [int] NOT NULL,
[TableAID] [int] NOT NULL,
[A21] [nvarchar](100) NOT NULL,
[A22] [int] NOT NULL
);
CREATE TABLE [dbo].[ATTR_B](
[ID] [int] NOT NULL,
[TableAID] [int] NOT NULL,
[A21] [nvarchar](100) NOT NULL,
[A22] [int] NOT NULL
);
CREATE TABLE [dbo].[ATTR_C](
[ID] [int] NOT NULL,
[TableAID] [int] NOT NULL,
[A21] [nvarchar](100) NOT NULL,
[A22] [int] NOT NULL
);
CREATE TABLE [dbo].[ATTR_D](
[ID] [int] NOT NULL,
[TableAID] [int] NOT NULL,
[A21] [nvarchar](100) NOT NULL,
[A22] [int] NOT NULL
);
INSERT INTO TableA VALUES(1, 'test', 1);
INSERT INTO TableB VALUES(1, 'ATTR_C');
INSERT INTO ATTR_C VALUES (1, 1, 'Name', 2019);
INSERT INTO TableA VALUES(2, 'test2', 2);
INSERT INTO TableB VALUES (2, 'ATTR_A');
INSERT INTO ATTR_A VALUES (1, 2, 'Name 2', 2016);
```

Answer 1

You were told already, that this approach is the wrong one entirely. But if you have to stick with this, you might try this:
Your test scenario in a new database (carefull, if you use this database name already...)
USE master;
GO
CREATE DATABASE MyTestDb;
GO
USE MyTestDb;
GO
CREATE TABLE [dbo].[TableA](
[ID] [int] NOT NULL,
[Title] [nvarchar](100) NOT NULL,
[TableBID] [int] NOT NULL
);
CREATE TABLE [dbo].[TableB](
[ID] [int] NOT NULL,
[TableName] [nvarchar](100) NOT NULL
);
CREATE TABLE [dbo].[ATTR_A](
[ID] [int] NOT NULL,
[TableAID] [int] NOT NULL,
[A21] [nvarchar](100) NOT NULL,
[A22] [int] NOT NULL
);
CREATE TABLE [dbo].[ATTR_B](
[ID] [int] NOT NULL,
[TableAID] [int] NOT NULL,
[A21] [nvarchar](100) NOT NULL,
[A22] [int] NOT NULL
);
CREATE TABLE [dbo].[ATTR_C](
[ID] [int] NOT NULL,
[TableAID] [int] NOT NULL,
[A21] [nvarchar](100) NOT NULL,
[A22] [int] NOT NULL
);
CREATE TABLE [dbo].[ATTR_D](
[ID] [int] NOT NULL,
[TableAID] [int] NOT NULL,
[A21] [nvarchar](100) NOT NULL,
[A22] [int] NOT NULL
);
INSERT INTO TableA VALUES(1, 'test', 1);
INSERT INTO TableB VALUES(1, 'ATTR_C');
INSERT INTO ATTR_C VALUES (1, 1, 'Name', 2019);
INSERT INTO TableA VALUES(2, 'test2', 2);
INSERT INTO TableB VALUES (2, 'ATTR_A');
INSERT INTO ATTR_A VALUES (1, 2, 'Name 2', 2016);
GO
--I create an inlined table valued function where all attribute tables are returned as one set using UNION ALL
--The engine is smart enough, to avoid the call, if the parameter does not fit.
CREATE FUNCTION dbo.GetTheRightSet(#SetKey VARCHAR(10))
RETURNS TABLE
AS
RETURN
SELECT ID,TableAID,A21,A22 FROM dbo.ATTR_A WHERE #SetKey='ATTR_A'
UNION ALL
SELECT ID,TableAID,A21,A22 FROM dbo.ATTR_B WHERE #SetKey='ATTR_B'
UNION ALL
SELECT ID,TableAID,A21,A22 FROM dbo.ATTR_C WHERE #SetKey='ATTR_C'
UNION ALL
SELECT ID,TableAID,A21,A22 FROM dbo.ATTR_D WHERE #SetKey='ATTR_D'
GO
--This is how to use it
SELECT TableA.*
,TableB.*
,TheSet.*
FROM TableA
LEFT JOIN TableB ON TableA.TableBID = TableB.ID
OUTER APPLY dbo.GetTheRightSet(TableB.TableName) TheSet
GO
--Clean up (carefull with real data)
USE master;
GO
DROP DATABASE MyTestDb;