Types of Relationships

Types of Relationships

1. One to one

   • Example
     • Patient and a doctor
     • In a hospital medical records
   • One record in one table is linked to one other record in one other table
   • Not good practice and inefficient because every record applicable to one thing has to be individually linked, which is time consuming

2. One to many

   • One record in one table will have many links to another table with other data representations.
   • Example
     • A customer can be linked to many orders

3. Many to many

   • Very hard to implement
     • Another table is introduced converting it to one to many
   • When more than one thing can be linked from one table to another and visa versa
   • Examples
     • Rental videos/films, bikes, cars, etc.

4. Information is stored in sets of related tables based on the entities

5. Relationships built through shared common fields

6. Overcome the problems of storing everything in single tables

7. Entity relationship diagram

   • An entity relationship diagram (ERD) is a specialised graphic that shows the relationships between entities in a database