I couldn't find any offer for a SQL based database as a service. Register, get access to your (virtual) DB server and plug-in your web-application. Plus DoS protection, auto-scaling, ... Why doesn't exist such a service?
Is running your mySQL at AWS good enough?<p>have a look at here: <a href="http://developer.amazonwebservices.com/connect/entry.jspa?externalID=1663" rel="nofollow">http://developer.amazonwebservices.com/connect/entry.jspa?ex...</a><p>you get all what you have asked for and even more ;-)
Latency would be to high for most usage (retrieve a couple of rows a t a time). I would use it as the service is ALL my queries where taking 1 second and more on my own system, and about the same time (or better: less time) from the cloud.