In SQL, COMMIT and ROLLBACK are crucial commands used to control transaction behavior, ensuring data integrity and consistency. When you perform a series of operations that change the database, these commands help you manage whether those changes should be permanently saved or discarded. A transaction begins with the execution of commands that modify data, such as INSERT, UPDATE, or DELETE. After these commands, if everything is satisfactory and you want to keep the changes, you issue a COMMIT command. This makes all changes made during the transaction permanent in the database.
Conversely, a ROLLBACK command is used to reverse any changes made during the current transaction. If you encounter an error or find that the results are not what you expected, you can use ROLLBACK to undo all operations performed since the last COMMIT. It effectively restores the database to its state before the transaction began. For example, if you insert a record and then realize the data is incorrect, running ROLLBACK will remove that record without affecting anything prior to the transaction.
A practical scenario might involve transferring funds between two bank accounts. Suppose you deduct an amount from one account and then add it to another. If the first operation succeeds but the second fails due to an issue (like reaching the account limit), you would use ROLLBACK to ensure that the amount deducted from the first account isn't lost, preserving the integrity of the financial transaction. If both operations succeed, you can then issue a COMMIT to finalize the transaction, ensuring that both accounts reflect the new balances accurately. This way, COMMIT and ROLLBACK enhance the reliability of database transactions and help to manage errors effectively.