How does a rollback operation work in SQL?

A rollback operation in SQL undoes all the transactions that have not been saved to the database.

In SQL, a rollback operation is a process that is used to undo transactions that have not been saved to the database. This operation is particularly useful in situations where an error has occurred during the transaction process. The rollback operation ensures that the database remains in a consistent state, even when a transaction fails to complete successfully.

When a transaction is initiated in SQL, it enters into a temporary workspace. This workspace is where all the changes made during the transaction are stored. If the transaction is successful, these changes are saved to the database. However, if an error occurs during the transaction, the changes made in the temporary workspace are not saved to the database. Instead, the rollback operation is initiated.

The rollback operation works by restoring the database to its state before the transaction was initiated. It does this by using the log that is created at the start of each transaction. This log contains a record of the database state before the transaction was initiated. When a rollback operation is initiated, the changes made in the temporary workspace are discarded, and the database is restored to its state as recorded in the log.

In SQL, the ROLLBACK command is used to initiate a rollback operation. This command can be used at any point during a transaction to undo the changes made. It can also be used after a transaction has been completed to undo the changes made during the transaction. However, once a transaction has been committed using the COMMIT command, the changes made during the transaction cannot be undone using the ROLLBACK command.

In conclusion, the rollback operation in SQL is a crucial feature that ensures the consistency and integrity of the database. It allows for the undoing of changes made during a transaction, thereby preventing the database from being left in an inconsistent state due to failed transactions.