Error when left joining two databases (SQL Server) - sql

Question

I have a great problem with joining two MSSQL databases together (on the same server) using LEFT JOIN. I run this SQL from the database OLAB_DB and get the error:
The multi-part identifier "OLAP_DB.dbo.OLAP_invoice.UserID" could not be bound.
There seem to be a problem with the DB not being able to find itself, and I have no idea of how to solve this. I have double and triple checked the spelling and rewrote the SQL several times, but now I just have to give up and ask for help :(
This doesn't work:
SELECT TOP 200
COALESCE(LTRIM(RTRIM(contact_db.dbo.ContactTable.EmailAdr)),LTRIM(RTRIM(contact_db.dbo.CustomerTable.EmailAdr))) AS EMAIL,
OLAP_invoice.OrdreLinjeID AS ORDERNO
OLAP_invoice.SalgsPris AS PRICE,
OLAP_invoice.UserID AS CONTACTID
FROM OLAP_invoice,contact_db.dbo.CustomerTable
LEFT JOIN contact_db.dbo.ContactTable
ON OLAP_DB.dbo.OLAP_invoice.UserID = contact_db.dbo.ContactTable.UserID
WHERE contact_db.dbo.CustomerTable.ClientID = OLAP_invoice.ClientID
But skipping the left join and just getting data from the two different databases works just fine.
This works just fine:
SELECT TOP 200
LTRIM(RTRIM(contact_db.dbo.CustomerTable.EmailAdr)) AS EMAIL,
LTRIM(RTRIM(contact_db.dbo.ContactTable.UserID)) AS EMAIL2,
OLAP_invoice.OrdreLinjeID AS ORDERNO
OLAP_invoice.SalgsPris AS PRICE,
OLAP_invoice.UserID AS CONTACTID
FROM OLAP_invoice,contact_db.dbo.CustomerTable
WHERE contact_db.dbo.CustomerTable.ClientID = OLAP_invoice.ClientID
AND contact_db.dbo.ContactTable.UserID = OLAP_invoice.UserID
The reason I need the LEFT JOIN, is because some orders are not registered with a UserID (only ClientID).
I have checked the access rights and there is no problem to access the fields individually, the problem occurs when I have to compare the values in the LEFT JOIN and specifies the absolute path.
Do you have any idea of what can be wrong?

Answer 1

You can try this:
SELECT TOP 200 COALESCE(LTRIM(RTRIM(contact_db.dbo.ContactTable.EmailAdr)),LTRIM(RTRIM(contact_db.dbo.CustomerTable.EmailAdr))) AS EMAIL,
OLAP_invoice.OrdreLinjeID AS ORDERNO
OLAP_invoice.SalgsPris AS PRICE,
OLAP_invoice.UserID AS CONTACTID
FROM OLAP_invoice LEFT JOIN contact_db.dbo.ContactTable ON OLAP_DB.dbo.OLAP_invoice.UserID = contact_db.dbo.ContactTable.UserID, contact_db.dbo.CustomerTable
WHERE contact_db.dbo.CustomerTable.ClientID = OLAP_invoice.ClientID

Answer 2

You are selecting from OLAP_invoice, but joining to OLAP_DB.dbo.OLAP_invoice. You need to qualify the table exactly the same every time, or use an alias.
So either:
FROM OLAP_DB.dbo.OLAP_invoice
left join contact_db.dbo.ContactTable
on OLAP_DB.dbo.OLAP_invoice...
OR
FROM ROM OLAP_invoice
LEFT JOIN ontact_db.dbo.ContactTable
ON OLAP_invoice...
Or you could use an alias as well, less typing that way.
FROM OLAP_invoice OI
LEFT JOIN ontact_db.dbo.ContactTable CT
ON OI...

Answer 3

Personally, I try to avoid having multiple tables in my FROM without intentionally specifying the type of join.
I find something like this to be much more readable and maintainable :
SELECT TOP 200
COALESCE( LTRIM(RTRIM(con.EmailAdr)), LTRIM(RTRIM(cus.EmailAdr)) ) AS EMAIL,
i.OrdreLinjeID AS ORDERNO
i.SalgsPris AS PRICE,
i.UserID AS CONTACTID
FROM OLAP_invoice i
LEFT JOIN contact_db.dbo.CustomerTable cus ON cus.ClientID = i.ClientID
LEFT JOIN contact_db.dbo.ContactTable con ON con.UserID = i.UserID