Autonumber field

An autonumber column automatically generates a unique, automatically incremented number for each record. Autonumbers can be helpful when you need a unique identifier for each record, or when using a formula in the primary field. Note that the autonumber field is not designed to count the number of records in a table. When a record is deleted, the remaining records are not re-numbered. This can leave gaps in the numbering. To re-number an autonumber field (in order to remove gaps, for example), you can either delete and re-create an autonumber field, or convert the field to a different type and then back to autonumber.