Creates a bounding circle from the_geom_webmercator on cartodb

bounding circle on cartodb

SELECT 
  ST_Buffer(
    st_centroid(ST_Union(the_geom_webmercator)),
    st_distance(
      st_centroid(ST_Union(the_geom_webmercator)),
      ST_EndPoint(ST_LongestLine(
        ST_Union(the_geom_webmercator), 
        ST_Union(the_geom_webmercator)
      ))
    )
   ) as the_geom_webmercator
FROM table_name GROUP BY some_column