Raven,

To read from an SQL Database, try the Database Replication app from the app store, the documentation available is extensive and walks you through how to set this up, kudos to Jasper. To write to an SQL Database, there is not an app available, but you could expose a web service in your app that could be consumed by your SQL database, others may have additional ideas about custom Java programming that could accomplish this.....creating a webservice which provides Mendix app based data would be quick and easy and, although I haven't done this myself, it seems that most current SQL database servers can consume a web service.

Hope that helps.

Mike