@tomm sorry for the lack of clarity!
You should be able to pass in a dynamic number of points. The second code block is an example of a JavaScript query you can use to generate the GeoJSON data from whatever is returned for your SQL query. It just assumes your SQL query has a longitude column and latitude column.
You would set it up as another resource query, and then pass its data to the GeoJSON box using {{ yourJsQuery.data }}.
The basic structure code block was just to give an idea of what the output should ultimately look like and doesn't actually go anywhere in the app 
I've included a working example with some mock SQL data that you can play around with
GeoJSON-20focus (1).json