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Just two records are returned:
VendorID AddressID
-------- -------------
1 1
2 3
(2 row(s) affected)
We know, therefore, that our OUTER JOIN is working. Since there are only two records in the VendorAddress
table and three vendors are returned, we must be returning at least one row from the Vendors table that
didn’t have a matching record in the VendorAddress table. While we’re here, we’ll just verify that by
briefly adding one more column back to our vendors query:
SELECT v.VendorName, va.VendorID
FROM Vendors v
LEFT OUTER JOIN VendorAddress va
ON v.VendorID = va.VendorID
Sure enough, we wind up with a NULL in the VendorID column from the VendorAddress table:
VendorName VendorID
-------------------- --------------
Don’s Database Design Shop 1
Dave’s Data 2
The SQL Sequel NULL
(3 row(s) affected)
The vendor named “The SQL Sequel” would not have been returned if we were using an INNER or
RIGHT JOIN. Our use of a LEFT JOIN has ensured that we get all vendors in our query result.
Now that we’ve tested things out a bit, let’s return to our original query and then add in the second
JOIN to get the actual address information. Because we don’t care if we get all addresses, no special
JOIN is required — at least, it doesn’t appear that way at first . . .
SELECT v.VendorName, a.Address
FROM Vendors v
LEFT OUTER JOIN VendorAddress va
ON v.VendorID = va.VendorID
JOIN Address a
ON va.AddressID = a.AddressID
We get back the address information as expected, but there’s a problem:
VendorName Address
--------------------------- ---------------
Don’s Database Design Shop 1234 Anywhere
Dave’s Data 567 Main St.
(2 row(s) affected)
Chapter 4: JOINs
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