Access 2007 for Starters: The Missing Manual

The Primary Key

Design view also allows you to set a table's primary key, which is a field (or a combination of fields) that's unique for each record. Every table must have a primary key. To understand why the primary key's important, you need to consider a little bit more about how databases work. The box "How Access Prevents Duplicate Records" in Section 2.4.1 has the full story.

Choosing a primary key is trickier than it seems. Imagine you have a list of friends (and their contact information) in a table named People. You may logically assume that you can create a primary key using a combination of first and last name. Unfortunately, that just won't do—after all, some address books have two Sean Smiths.

Your best solution's to invent a new piece of information. You can label every individual in your contact list with a unique ID number. Best of all, you can get Access to automatically create this number for you (and make sure that no two people get the same number), so you don't even need to think about it. That way, if you have two Sean Smiths, each one has a different ID. And even if Ferris Wheel Simpson decides to change his first name, the ID remains the same.

UP TO SPEED: How Access Prevents Duplicate Records

In order to function correctly, a database program like Access needs to be able to tell the difference between each and every record in your table. In other words, you can't insert two records with exactly the same information. Databases are notoriously fussy, and they ...