Database relationships

Relationships between database

Entities can be linked between databases, this is called a relationship.

Types of relationships

One-to-one Examples of such a relationship include the relatIonship between Husband and Wife, Country and Prime Minister.
One-to-many Examples include the relationship between Father and Child, Costumer and Order.
Many-to-many Examples include the relationship between Student and Course, Stock Item and Supplier, Film and Actor.

Relationships can be modelled using an entity relationship diagram.

There are a few concepts with a relational database.

A foreign key is a attribute that has been linked to an external table. The foreign key is the primary key an another database.