Connecting Presto to a relational database is a tricky question. If you just want to have Presto scan the table and perform all computation in Presto, it is pretty easy, but for this to perform well, you would want to push down some of the computation to the database. The other problem is if you only have one database, you would have hundreds of cores hammering that single database for data.

That said, earlier this year, during a hackathon, we build a prototype connector that could split a query and push down the relevant parts to a distributed database that supports simple aggregations. It would be more work to clean this up and integrate, so if a lot of people are interested in this we can prioritize that.

The data still lives in HDFS, so Sqoop is the preferred way to export to RDBMS as far as I know.