Database Reference
In-Depth Information
10
Joining Tables
In this chapter:
What is a join?
What is Oracle's proprietary format for joins?
What is the ANSI join format?
What types of joins can be performed?
How can joins be implemented?
A join is retrieval of data from more than one table. This chapter shows
you how to merge rows from multiple tables into a single query. Merging of
rows is known as a
. This chapter experiments with example SELECT
statements containing many different types of joins.
In previous chapters you have explored the SELECT, FROM, WHERE,
and ORDER BY clauses. Both the American National Standards Institute
(ANSI) format JOIN clause and the Oracle proprietary format for joining
tables are used in all examples where possible. The JOIN clause is the ANSI
equivalent of the Oracle proprietary join syntax. We examine both formats
for the following reasons:
join
The Oracle proprietary format has not as yet been deprecated in favor
of the ANSI JOIN clause; therefore, it is important that even new
DBAs be familiar with its use. As a side issue, Oracle Certification
exams may test both formats.
Both formats are useful for explaining how joins behave and how to
select the most appropriate format. In addition, one type of join, the
