Release 10.1A: OpenEdge Getting Started:
Database Essentials

Table relationships

In a relational database, tables relate to one another by sharing a common column or columns. This column, existing in two or more tables, allows the tables to be joined. When you design your database, you define the table relationships based on the rules of your business. The relationship is frequently between primary and foreign key columns; however, tables can also be related by other nonkey columns.

In Figure 2–1, the Customer and Order tables are related by a foreign key, Customer Number.

Figure 2–1: Relating the Customer and Order Tables

If the Customer Number is an index in both tables, you can do the following very quickly:

Find all the orders for a given customer and query information (such as order date, promised delivery date, the actual shipping date) for each order.
Find customer information (such as name and address) for each order using an order’s customer number.