|
AutoNumber is a type of data used in Microsoft Access tables to generate an automatically incremented numeric counter. It may be used to create an identity column which uniquely identifies each record in a table. Only one AutoNumber field is allowed in each table. The data type was called Counter in Access 2.0. == Forms == There are three forms in which AutoNumbers can be generated: ;start value plus increment: AutoNumbers generated by this mechanism start with the start number and increment with the increment value, checking for collision with existing table rows.〔 ;random: AutoNumbers generated by this mechanism are assigned using a pseudo-random number generator that generates long integers and checks for collisions with existing table rows.〔 ;replication IDs: AutoNumbers generated by this mechanism are IDs generated in a manner to make it highly improbable that collisions will occur.〔 They are Microsoft Globally Unique Identifiers, and the probability of collision is low until the year AD 3400. The default size of an AutoNumber is a 4-byte (long) integer. This is the size used for start+increment and random AutoNumbers. For replication ID AutoNumbers, the FieldSize property of the field is changed from long integer to Replication ID.〔If an AutoNumber is a long integer, the NewValues property determines whether it is of the start+increment or random form. The values that this property can take are "Increment" and "Random".抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「AutoNumber」の詳細全文を読む スポンサード リンク
|