Release 10.1A: OpenEdge Reporting:
Query/Results for UNIX

> ## Table relationships

> The most powerful advantage an electronic filing system has over a paper filing system is that it can process data based on the relationship between database tables. The relationship is based on shared data. For example, let us take a look at a database table that contains information about orders placed by customers. Each record in the order table might contain fields such as the number of the order, the promised delivery date, etc., as shown in Figure 1–4.

> However, to relate the Order table to the Customer table, the order table must contain one field that is already in the Customer table. Since the customer number field uniquely identifies each customer, it is the most appropriate field. When a database uses common data (identical field name with identical data) to relate tables to each other, it is called a relational database.

> With relationships between tables established, you can perform extensive searchers or queries. For example, you can query all the customers whose orders are promised before November 2001 or the number of outstanding orders by sales region. Imagine how tedious this search can be if you are using a paper filing system.

> Figure 1–4: Relationship between customer and order records

> By default, Results relates two tables if one of the tables has a unique index and all fields in that unique index appear in the other table. For information on defining relationships between tables, see Chapter 9, " Database Administration."

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