relationships

relationships

1. one to one

   • one set of deatils
   • one record is linked to another table this can be quite inefficent
   • e.g. a husband only has one wife

2. one to many

   • a customer can be link to many orders

3. many to many

   • very hard to implement so you introduce another table and split it down
   • more than one thing to another table with many things

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 sorting everything in single tables

7. an entity relationship diagram (ERD) is a specialised graphic that's shows the relationship between entity in a database