Multi-part identifer issue when joining table to function - sql

Question

THE QUESTION:
My join is not working as expected:
join db1.function1(t1.id) f1 on f1.id = t1.id
The error message is:
Incorrect syntax near '.'.
The multi-part identifier 't1.id' could not be found.
This bit (t1.id) is underlined with a red squiggly line.
I get the same issue when I try to use cross apply.
The function is a table-valued function, so returns a table.
FULL QUERY EXAMPLE:
select t1.*, f1.*
FROM db1.dbo.table1 t1
join db1.dbo.function1(t1.id) f1 on f1.id = t1.id
SIMPLIFIED VERSION OF THE FULL FUNCTION:
USE [DB1]
ALTER FUNCTION [dbo].[function1](#id int)
RETURNS #return_table TABLE (
id INT,
col1 INT,
col2 VARCHAR(255)
)
AS
BEGIN
-- ...
-- do all sorts of stuff here to get needed data, temp tables, unions, joins, inserts, selects etc
-- ...
INSERT INTO #return_table (id, col1, col2)
select distinct id, col1,
(
select isnull(cast(col2 as varchar(3)),'NULL')+','
from #tbl2 t2
where t2.id = t1.id
for xml path('')
) col2
from #tbl1 a1
RETURN;
END;

Answer 1

Hi So basically you are looking to perform a INNER JOIN. The problem you are fasing is that you are using a Function. What you should be using to achieve is a CROSS JOIN. If left Join is desired, you could use a OUTER JOIN
There is a great artical that explains in detail that has helped me in the past and can be navigated to by following this link. ClickMe. Search for Use case 5: APPLY and TVFs
I have also written a code that may be of some assistance for the immediate request
Test Data:
IF OBJECT_ID(N'Test1')>0
BEGIN
DROP TABLE Test1
END
CREATE TABLE Test1 (Tbl1ID INT IDENTITY(1, 1),
Name VARCHAR(250))
INSERT INTO Test1
VALUES('ABCD1'),
('ABCD2'),
('ABCD3'),
('ABCD4'),
('ABCD5'),
('ABCD6')
IF OBJECT_ID(N'Test2')>0
BEGIN
DROP TABLE Test2
END
CREATE TABLE Test2 (Tbl2ID INT IDENTITY(1, 1),
Name VARCHAR(250))
INSERT INTO Test2
VALUES('ABCD1'),
('ABCD2'),
('ABCD4'),
('ABCD5')
GO
TV Function:
IF EXISTS (SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'[dbo].[ufn_TVFTable2]') AND type in (N'FN', N'IF', N'TF', N'FS', N'FT'))
DROP FUNCTION [dbo].[ufn_TVFTable2]
GO
CREATE FUNCTION ufn_TVFTable2 (#Name NVARCHAR(1000))
RETURNS TABLE
AS
RETURN
SELECT *
FROM Test2
WHERE Name = #Name
GO
Usage:
SELECT t.*,tf.*
FROM Test1 AS T
CROSS APPLY dbo.ufn_TVFTable2(T.name) AS tf
Cleanup:
IF EXISTS (SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'[dbo].[ufn_TVFTable2]') AND type in (N'FN', N'IF', N'TF', N'FS', N'FT'))
DROP FUNCTION [dbo].[ufn_TVFTable2]
GO
IF OBJECT_ID(N'Test1')>0
BEGIN
DROP TABLE Test1
END
IF OBJECT_ID(N'Test2')>0
BEGIN
DROP TABLE Test2
END
Your Query would look like below:
SELECT t1.*,
f1.*
FROM db1.dbo.table1 AS t1
CROSS APPLY db1.dbo.function1(t1.id) AS f1
Usage Example 2:
;WITH cte_table1(ID) AS
(
SELECT 82938382 AS ID UNION ALL
SELECT 82938383 AS ID UNION ALL
SELECT 82938384 AS ID UNION ALL
SELECT 82938385 AS ID
)
SELECT t1.*,
f1.*
FROM db1.dbo.table1 AS t1
CROSS APPLY db1.dbo.function1(t1.id) AS f1

Answer 2

You are trying to join onto a function using a column from table1 before the join has actually happened. Think of the return of function1 as an atomic operation which you are then joining to table1. So at that point, SQL doesn't know what the value of the id column is.
Assuming function1 does not return a table, you probably wanted to do this:
SELECT t1.*, db1.dbo.function1(t1.id)
FROM db1.dbo.table1 t1