The SQL Programming Language

Chapter 2

Entities andRelationships

2.1    Foreign Keys and Relationships between Tables

When a database is designed correctly, information about different kinds of entities is stored in separate tables. The relationships between the entities in different tables are as important as the attributes of the entities themselves. The Actor and Role tables, as introduced in Chapter 1, contained no information telling which actor played which role. In contrast, Table 2.1 shows the Role table expanded to include an actorID column, which captures the relationship between the Actor and Role tables.

TABLE 2.1 Role

Given a Role table containing an actorID ...