Database Reference
In-Depth Information
10. Table Relationships
There is no substitute for the comfort supplied by the utterly taken-for-granted
relationship.
—I
RIS
M
URDOCH
Topics Covered in This Chapter
Youlearnedin
Chapter3
,
“
Terminology
,
”thata
relationship
existsbetweentwotableswhen
you can in some way associate the records of the first table with those of the second. You
also learned that each relationship has three distinct characteristics: the type of relationship
thatexistsbetweenthetables,themannerinwhicheachparticipates,andthedegreetowhich
each table participates.
In this chapter, I'll discuss these topics in more detail. You'll first learn how to identify and
establishtherelationshipsbetweenthetablesinadatabaseandthenhowtoseteachrelation-
ship's characteristics. You'll also learn how to diagram tables and relationships, which will
enable you to create a graphic representation of the entire database structure.
Why Relationships Are Important
A relationship is an important component of a relational database.
•
It establishes a connection between a pair of tables that are logically related to
each other.
A pair of tables is logically related via the data each contains. For ex-
ample, consider the tables in
Figure 10.1
.
