Google has announced their Cloud SQL API.
Up till now, Google has only offer Datastore API on App Engine. Datastore is based on big table database, and is unlike the more commonly known MySql database.
With this Cloud SQL, Google is offering a MySql database on their infrastructure. It is simple to use. Simply setup an instance, and do your SQL in Java or Python!
This API is currently in Beta and is free. It will be paid someday.