OutSystems integrates with external databases, making it possible to use data from those databases in your OutSystems applications.
For this, you can use the Connect to External Table or View wizard in Integration Studio. It automatically creates a connector to the external database and allows you to use the data from the external database in a transparent way, by defining entities and entity attributes that you can use in Service Studio as part of the application data layer.
For the list of supported external databases, check the System Requirements.
The import process has several steps done in different tools. Follow the instructions in Connect to an External Database that take you through all the required steps.