Is a MySQL statement from an external script possible?
Drupal does use SQL statements to communicate with the database, however it does so through a built in abstraction layer. That said, you can write regular old SQL from any PHP script to query the information you need, as long as you have the database connection info. Personally I would build whatever functionality you're after into a custom Drupal module, and then use that to interface with whichever external service you're working with. We would need a bit more information on exactly what you're trying to achieve to provide more specific feedback however.