As a feature request, I think it would be very useful to have a drop down to select the database, then a separate drop down to select the X series and a separate value to select the Y series, or xquery functions to generate either of these :)
That’s probably out of scope, and it introduces challenges we cannot control that easily (such as inefficient queries that slow down rendering a lot; descendant elements might have attributes with identical names; etc.). One feature we might support one day is the ad-hoc visualization of query results.