A transaction is a unit of work that is performed against a database. Transactions are units or sequences of work accomplished in a logical order, whether in a manual fashion by a user or automatically by some sort of a database program.
There are following commands used to control transactions:
COMMIT: to save the changes.
ROLLBACK: to rollback the changes.
SAVEPOINT: creates points within groups of transactions in which to ROLLBACK
SET TRANSACTION: Places a name on a transaction.
Transactional control commands are only used with the DML commands INSERT, UPDATE and DELETE only. They can not be used while creating tables or dropping them because these operations are automatically commited in the database.