Backup, Empty and Import databases with Drush in Drupal
Create a backup.
drush sql-dump > /path/to/folder/backup.sql
Empty the database tables
drush sql-drop
Import the tables
drush sql-cli < /path/to/folder/backup.sql
drush sql-dump > /path/to/folder/backup.sql
drush sql-drop
drush sql-cli < /path/to/folder/backup.sql