From Higher Computing Science
- A one-to-one relationship means that a foreign key links a record to one other record.
- A one-to-many relationship means that a foreign key links one record to more than one record in another table. This may be useful, for example, if details of an author are stored in one table, and a list of books is stored in the other. One author will be linked to many books.
- A many-to-many relationship means that a items in one table are links to items in another table via a mapping table, which consists only of the keys of the two tables.