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Chapter 4. Relationships: Your Key to Da... > Examining Indexes and Relationships

Examining Indexes and Relationships

The field that joins two tables on the one side of a one-to-many relationship must be a primary key field or have a unique index so that referential integrity can be maintained. 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.

An index on the field on the many side of the one-to-many relationship is optional. It improves the performance of any processing involving 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.


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