As Kyle said, you cannot directly access the database.  

If you need to provide ongoing access for customers or suppliers, for instance, you can create a REST API that will enable people to read (and change, if needed) the information in your app.

Hi François,

Unfortunately it is not possible to connect directly to the database for an application hosted in the Mendix Cloud.

The most direct indirect way would be through the database backups that are created nightly or manually and then restoring that backup on a PostgreSQL server that you can directly access. Instructions to do that can be found in the Mendix documentation: Restoring a Backup Locally | Mendix Documentation