The Primary Key

There is one more field that should be added to all tables: the Primary Key. The primary key uniquely identifies each record. A Primary Key cannot be empty, or null. The value entered for the Primary Key cannot be duplicated.

 

Some organizations use a special numbering system. For example, many medical databases use the Social Security number to identify their patients. Each of us has our own unique, social security number. However, there are several identity and security concerns about using social security numbers.

 

In Microsoft Access the Primary Key can be an AutoNumber. As you add new records, Access will provide the next sequential number automatically.

 

Databases crunch numbers quickly. If the Primary key is text, such as a social security number, then each character must be evaluated by the database one at a time. This process is very slow.