9. Changing a many-to-many into a one-to-many relationship

A many-to-many relationship is not a good idea when designing database relationships.

To overcome this, an extra entity is usually added to the database design which then allows the relationship to become a many-to-one or a one-to-many relationship.

Remember our example on the previous page

many to many relationship

A third entity can be added called 'rentals'.

Thus the relationship becomes:

Customers can have many different rentals

A rental belongs to one customer


A video can be rented many times

Many rentals can contain that video


rental entity


Challenge see if you can find out one extra fact on this topic that we haven't already told you

Click on this link: Entity Relationship Diagram


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