Primary And Foreign Keys
Primary keys
The primary key is a field that uniquely identifies each record.
Example
-
Everyone has a unique SQA candidate number.
-
Cars have a unique registration.
At National 5 you need to be able to identify the primary key from a given table.
Foriegn Keys
When a field from one table or entity appears in another table or entity, it is called a foreign key.
The foreign key is a field that both tables have in common.
Example
- MovieID is the primary key for Movie,
and
- DirectorID is the primary key for Director.
Because DirectorID - the primary key from Director - also appears in the Movie table, that makes it a foreign key.