ASA SQL User's Guide
  Adding, Changing, and Deleting Data
    Data modification statements

Transactions and data modification

When you modify data, the transaction log stores a copy of the old and new state of each row affected by each data modification statement. This means that if you begin a transaction, realize you have made a mistake, and roll the transaction back, you also restore the database to its previous condition.

For more information about transactions, see Using Transactions and Isolation Levels.