What is the purpose of the ROLLBACK command in SQL?

The ROLLBACK command in SQL is used to undo transactions that have not yet been saved to the database.

In more detail, the ROLLBACK command is a transactional control language command that is used in SQL to undo transactions that have not yet been saved to the database. It is a very important command and is used to ensure data integrity by cancelling out erroneous or unwanted transactions before they are permanently written into the database.

When a transaction is initiated in SQL, it is in a pending state until it is either committed to the database using the COMMIT command, or undone using the ROLLBACK command. If a transaction is rolled back, all the changes made in the transaction are discarded and the database is returned to its state before the transaction began.

The ROLLBACK command is particularly useful in situations where a transaction may involve multiple changes to the database, and an error occurs partway through. Instead of having to manually undo each change, the ROLLBACK command can be used to automatically discard all changes made in the transaction.

For example, consider a banking application where a transaction involves transferring money from one account to another. If an error occurs after the money has been deducted from the first account but before it has been added to the second, the ROLLBACK command can be used to undo the deduction and prevent the money from disappearing.

In addition to rolling back entire transactions, SQL also allows for the use of savepoints within a transaction. A savepoint is a specific point in a transaction that you can roll back to without rolling back the entire transaction. This can be useful in long, complex transactions where you might want to save your progress at certain points and be able to undo changes from that point forward if necessary.

In conclusion, the ROLLBACK command is a powerful tool in SQL that helps maintain data integrity by allowing for the undoing of transactions before they are permanently written into the database. It is an essential command for any SQL developer to understand and use effectively.