Database - How To Movies
 
1. Setting up and creating tables and fields 2. Formatting Fields. 3. Creating Primary Key and Relationships 4. Searching and Creating Reports 5. Editing Reports
 
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Database

Relationships

When a DVD is rented, a link is made between DVD RENTAL and MEMBER. This is called a relationship. Each member can rent out many DVDs, but each DVD can only be rented by one member at a time, so we say there is a one-to-many relationship between MEMBER and DVD RENTAL.


This is sometimes written as... MEMBER 1:M DVD RENTAL


1:M stands for one-to-many.

Below a diagram shows of the relationship between MEMBER and DVD RENTAL. This is called an entity-relationship diagram. The line joining the entities is called a crow’s foot, and the ‘toes’ are at the ‘many’ end of the relationship.

There can be other types of relationship between entities. For example, every vehicle has a registration number, and each registration number corresponds to a single vehicle, so there is a one-to-one relationship between VEHICLE and REGISTRATION NUMBER.

In a school, each pupil has many teachers, and each teacher teaches many pupils, so there is a many-to-many relationship between PUPIL and TEACHER.


These relationships can be written as:


VEHICLE 1:1 REGISTRATION NUMBER
PUPIL M:N TEACHER


M:N stands for many-to-many (the number of teachers and pupils may be different, which is why N is used instead of M)

 

 



 

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