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

A third entity can be added called 'rentals'.

Thus the relationship becomes:

Customers can have many different rentals

A rental belongs to one customer

AND

A video can be rented many times

Many rentals can contain that video