I think this should return a special class to represent the result set. The reason is that a tuple will be harder to work with in Java, and will also be harder to extend if we want to return more information over time.

Also, the doc comment for this method should say that it's going to collect the data and return it locally (as opposed to sql2rdd). It may also be good to just call it "runSql" or "execute" if those aren't taken.