- Why This Chapter Is Important
- Introduction to Relational Database Design
- Establishing Relationships in Access
- Establishing Referential Integrity
- Looking at the Benefits of Relationships
- Examining Indexes and Relationships
- Practical Examples: Establishing the Relationships Between the Tables Included in the Time and Billing Database
The field that joins two tables on the one side of a one-to-many relationship must be a primary key field or must have a unique index so that the Jet Engine can maintain referential integrity. If the index on the one side of the relationship is not unique, there is no way to determine to which parent a child record belongs.
In Access 2003, it is not necessary to create an index for the field on the many side of the relationship. Access 2003 will create an internal index for you. If you do create an index on the many side of the relationship, make sure that you set the index to Yes (Duplicates OK); otherwise, you will have a one-to-one, rather than a one-to-many, relationship.