When a connection is operating in implicit transaction mode, the instance of the SQL Server Database Engine automatically starts a new transaction after the current transaction is committed or rolled back. You do nothing to delineate the start of a transaction; you only commit or roll back each transaction. Implicit transaction mode generates a continuous chain of transactions.
After implicit transaction mode has been set on for a connection, the instance of the Database Engine automatically starts a transaction when it first executes any of these statements:
The transaction remains in effect until you issue a COMMIT or ROLLBACK statement. After the first transaction is committed or rolled back, the instance of the Database Engine automatically starts a new transaction the next time any of these statements is executed by the connection. The instance keeps generating a chain of implicit transactions until implicit transaction mode is turned off.
Implicit transaction mode is set either using the Transact-SQL SET statement, or through database API functions and methods.
Under a multiple active result sets (MARS) session, a Transact-SQL implicit transaction becomes a batch-scoped transaction. If the batch-scoped transaction is not committed or rolled back when the batch completes, SQL Server automatically rolls back the transaction. For more information, see Controlling Transactions (Database Engine) and Transactions (Transact-SQL).