Problem

When trying to restore a backup over an existing database, the following error appears:

RESTORE DATABASE is terminating abnormally. The tail of the log for the database "DATABASE_NAME" has not been backed up. 

Use BACKUP LOG WITH NORECOVERY to backup the log if it contains work you do not want to lose.

Solution

 Check if the database is in full recovery model. If it is, the message warns that if the database is restored, there are transactions that will be lost.

...

 If this is not a concern, you can change the recovery model from full to simple or you can do the restore with REPLACE option. After this modification, the restore will complete successfully.