They're using SQLAlchemy as a database abstraction layer which supports MySQL out of the box.

So, you just need to set the config param SQLALCHEMY_DATABASE_URI like this:

https://github.com/airbnb/caravel/blob/1b4e750b2aa111445703d...

The configuration guide explains it further:

https://github.com/airbnb/caravel/blob/master/docs/installat...