If you are just starting with Access, chances are you are using the Table Wizard to help construct tables. One of the nice things about the Wizard is that it can automatically define a primary key for you. The Wizard is great for getting going, but once you become more comfortable with databases in general, you will likely build all of your tables using Design view. Access doesn’t ask to assign a primary key until you are ready to close and save the table, but you can specify one whenever you like right inside design view. Consider the following table:

  

  

If we close the table now, Access will ask to create a primary key, which it does by creating another field like VehicleID. But VehicleID is already a fine candidate for a primary key. To make it the primary key, right-click the grey box beside the VehicleID cell and click Primary key:

 

 

Primary keys in tables are denoted by a small key in the grey box beside the cell name: