.Microsoft Access provides the AutoNumber data type to create fields that automatically enter a number when a record is added. Once a number is generated for a record, it can't be deleted or changed. An AutoNumber field can generate three kinds of numbers: sequential numbers that increment by one, random numbers, and Replication ID (also referred to as GUIDS — globally unique identifiers) numbers. AutoNumbers that increment by one are the most common kind of AutoNumber and are a good choice for use as a table's primary key. Random AutoNumbers will generate a random number that is unique to each record within the table. Replication ID AutoNumbers are used in database replication to generate unique identifiers for synchronizing replicas.
For more information on creating an AutoNumber field, click .