Can I efficiently sum/count total clicks/conversions from a separate table?

I am not sure what you are trying to ask but if you are asking how to get your google assistant to ask questions (and act on the replies perhaps?). You do so by building Google Actions. Google Actions are just like mobile apps but is made available in Google Assistant when a user ask for a particular action via an Invocation such as Ok Google, Talk to Keep Count. The Google Action called Keep Count would then take over. There in the action you can program it so that the google assistant interact with the user via a series of question and replies. You can find out how to do Google Action by visiting the Google Assistant developer website at https://developers.google.com/assistant. Happy to jump on a call if you need more specific directions. I am an expert in the field of Voice Technology. You can also learn from live streams on twitch at twitch.tv/goldzulu. Hope that helps.

Can you describe the data in the table? I can think of a few solutions, most if which are based on the data you are storing. For example, chances are when you have large tables you are probably not doing any summarization of your data. If possible pre-compute the result and spit out the answer from a shorter table or cache (a cache which is generate at the time of the summary being generated, only useful if you often request this data shortly after it being created - doesn't sound like you needed to do this though) Another alternative would to be consider archiving of data. Is all the data required all the time? If not then consider a means of removing data you don't need (after x period of time) or switching to a new shard / table periodically. The other, more obvious, I would mention are to reconsider your existing indexes or partitioning your tables, if you have not done this already. You can start manually sharding tables across servers based on a hash of some kind but your Db is still relatively small (assuming you can summarize some of your data) and should not need this yet.

Here is an article about setting up AWS EC2 to run Play and Mongo: http://stevenwilliamalexander.wordpress.com/2012/06/10/amazon-ec2-mongo-play-scala-instance-setup-gu/ and there are also guides for binding to Amazon Simple DB and Dynamo in Scala as well that might be much easier setup than using MySQL. I've used a lot of AWS services for building composite services and I'm available for a call if you get stuck or need any advice on best practices.