Beginning SQL

7
Selecting Data from
Different Tables
In Chapter 3, you learned how to use inner joins to create results sets formed from more than one
table. In this chapter, to use the words of Chef Elzar from Futurama, you take it up a notch and
look at how you can deal with more complex problems using more sophisticated inner joins, and
you also something you’ve not yet encountered: outer joins. Ultimately, this chapter is all about
finding a way to get the data you need to answer a question, and you can expect to see lots of
practical examples in this chapter.
Joins Revisited
In Chapter 3, you learned about inner joins and how they enable you to retrieve related data from
different tables and display that data in one results set.
Remember, an inner join consists of the INNER JOIN keyword, which specifies which two tables
are to be joined. After the INNER JOIN keyword, you specify an ON clause, which identifies the
condition that must be true for a row from each table to be included in the final joined results. The
basic syntax of an inner join is as follows:
name_of_table_on_left INNER JOIN name_of_table_on_right
ON condition
For example, the Attendance table doesn’t contain the name and address of each person attending
a meeting; rather, it contains only the MemberId. However, the MemberDetails table contains
matching MemberIds as well as members’ full details. So if you want to produce results that contain
a meeting date and the name of the member attending, you’d have to create a SELECT statement
(similar to the following) that produces a results set joining the two tables together:
SELECT MeetingDate, FirstName, LastName
FROM Attendance INNER JOIN MemberDetails
ON Attendance.MemberId = MemberDetails.MemberId;