MDAC 2.5 SDK - ODBC Programmer's Reference
Chapter 14: Transactions
In auto-commit mode, every database operation is a transaction that is committed when performed. This mode is suitable for many real-world transactions that consist of a single SQL statement. It is unnecessary to delimit or specify completion of these transactions. In databases without transaction support, auto-commit mode is the only supported mode. In such databases, statements are committed when they are executed and there is no way to roll them back; they are therefore always in auto-commit mode.
If the underlying DBMS does not support auto-commit mode transactions, the driver can emulate them by manually committing each SQL statement as it is executed.
If a batch of SQL statements is executed in auto-commit mode, it is data source–specific when the statements in the batch are committed. They can be committed as they are executed or as a whole after the entire batch has been executed. Some data sources may support both of these behaviors and may provide a way of selecting one or the others. In particular, if an error occurs in the middle of the batch, it is data source–specific whether the already-executed statements are committed or rolled back. Thus, interoperable applications that use batches and require them to be committed or rolled back as a whole should execute batches only in manual-commit mode.