An employee and his or her employment details form a record in the Employees table. This information should not be repeated in other tables or other records.
You may have heard that no two snowflakes are alike—this characteristic also applies to records in a well-structured database.
Each record in each table should be unique—in other words, you wouldn't have two identical records about Nancy Davolio in the same database. But what if you have two employees named Nancy Davolio?
To distinguish one record from another, tables can contain a primary key field.
The primary key is an identifier—such as a part number, a product code, or an employee ID—that's unique to each record.
The primary key should be a piece of information that won't change frequently.
If you want, Access can assign a numeric primary key that increases by 1 each time you add a record to a table. This number continues to be associated with this record, even if you add and delete other records entered before this record in your database.
If the primary key is a number, how will people recognize the record? Don't worry, the database can associate each primary key with a friendly name, such as an employee's name. That way, you can work with familiar information, even though the underlying table is storing a number.