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

Now, look at the heart of what’s returned (you’ll see some one row(s) affecteds in there — just ignore
them until you get to where the results of your query are visible):
col2
----
AAA
BBB
CCC
DDD
EEE
(5 row(s) affected)
Divider Line-------------------------col2
----
AAA
BBB
CCC
CCC
DDD
EEE
(6 row(s) affected)
The first result set returned was a simple UNION statement with no additional parameters. You can see
that one row was eliminated. Even though we inserted “CCC” into both tables, only one makes an
appearance since the duplicate record is eliminated by default.
The second return changed things a bit. This time we used a UNION ALL and the ALL keyword ensured
that we get every row back. As such, our eliminated row from the last query suddenly reappears.
Summary
Chapter 4: JOINs
In an RDBMS, the data we want is quite frequently spread across more than one table. JOINs allow us to
combine the data from multiple tables in a variety of ways:
❑ Use an INNER JOIN when you want to exclude non-matching fields.
❑ Use an OUTER JOIN when you want to retrieve matches wherever possible, but also want a
fully inclusive data set on one side of the JOIN.
❑ Use a FULL JOIN when you want to retrieve matches wherever possible, but also want a fully
inclusive data set on both sides of the JOIN.
❑ Use a CROSS JOIN when you want a Cartesian product based on the records in two tables. This
is typically used in scientific environments and when you want to create test data.
❑ Use a UNION when you want the combination of the result of a second query appended to the
first query.
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