Beginning Microsoft SQL Server 2008 ... - S3 Tech Training

Chapter 4: JOINs
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Somehow, we lost one of our vendors. That’s because SQL Server is applying the rules in the order that
we’ve stated them. We have started with an OUTER JOIN between Vendors and VendorAddress. SQL
Server does just what we want for that part of the query — it returns all vendors. The issue comes when
it applies the next set of instructions. We have a result set that includes all the vendors, but we now
apply that result set as part of an INNER JOIN. Because an INNER JOIN is exclusive to both sides of the
JOIN, only records where the result of the first JOIN has a match with the second JOIN will be included.
Because only two records match up with a record in the Address table, only two records are returned in
the final result set. We have two ways of addressing this:
❑ Add yet another OUTER JOIN
❑ Change the order of the JOINs
Let’s try it both ways. We’ll add another OUTER JOIN first:
SELECT v.VendorName, a.Address
FROM Vendors v
LEFT OUTER JOIN VendorAddress va
ON v.VendorID = va.VendorID
LEFT OUTER JOIN Address a
ON va.AddressID = a.AddressID
And now we get our expected result:
VendorName Address
--------------------------- ------------
Don’s Database Design Shop 1234 Anywhere
Dave’s Data 567 Main St.
The SQL Sequel NULL
(3 row(s) affected)
Now do something slightly more dramatic and reorder our original query:
SELECT v.VendorName, a.Address
FROM VendorAddress va
JOIN Address a
ON va.AddressID = a.AddressID
RIGHT OUTER JOIN Vendors v
ON v.VendorID = va.VendorID
And we still get our desired result:
VendorName Address
--------------------------- --------------
Don’s Database Design Shop 1234 Anywhere
Dave’s Data 567 Main St.
The SQL Sequel NULL
(3 row(s) affected)