Restoring a database backup returns the database to the same state it was in when the backup was created. Any incomplete transactions in the database backup, (transactions that were not complete when the backup operation completed originally), are rolled back to ensure the database remains consistent.

Restoring a transaction log backup reapplies all completed transactions that are in the transaction log to the database. When applying a transaction log backup, SQL Server reads forward through the transaction log, rolling forward all the transactions on the transaction log. When SQL Server reaches the end of the transaction log, it has re-created the exact state of the database at the time the backup operation started. The restore operation then rolls back all transactions that were incomplete when the backup operation started.