A field data type that automatically stores a unique number for each record as it's added to a table. Three kinds of numbers can be generated: sequential (increment by 1), random, and Replication ID (used by the Replication Manager to ensure the integrity of data in replicated databases). Numbers generated by an AutoNumber field can't be deleted or modified.
Note For replicated databases, an AutoNumber field is not incremented by 1. Instead, it is assigned a random value between -2,000,000,000 and 2,000,000,000.