Progress
Results User’s Guide
for Windows


Types of Relationships

You can create three types of relationships among tables: one-to-one, one-to-many, many-to-many. The following sections describe these relationships.

One-to-one Relationship

A one-to-one relationship occurs when one record can relate to one and only one instance of a record in another table. For example, a business might decide to assign one office to exactly one employee. Thus, one employee can have only one office. The same business might also decide that a department can have only one manager. Thus, one manager can manage only one department. Figure 1–7 illustrates this relationship.

Figure 1–7: One-to-one Relationships

One-to-many Relationship

A one-to-many relationship occurs when one record can relate to multiple records in another table. For example, one customer can place many orders, one student can take many courses, and a sales representative can have many customer accounts. Figure 1–8 illustrates this relationship.

Figure 1–8: One-to-many Relationships

Many-to-many Relationship

A many-to-many relationship occurs when multiple records can relate to multiple records in another table. Likewise, those related records have many records in the first table. For example, an order can contain many items, and an item can appear in many different orders; an employee can work on many projects, and a project can have many employees working on it. Figure 1–9 illustrates this relationship.

Figure 1–9: Many-to-many Relationships


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