I have a layer of points, which I want to group into multipoints grouping by some column. This part is easy:
SELECT name_pre, CastToMulti(GUnion(geometry)) AS geometry FROM sp_survey GROUP BY name_pre;
But the trick is that I'd like to assign to each part of multipoint incrementing m value (0, 1, 2 etc.) based on the "depth" column in sp_survey table, ordered from lowest (0) to highest (n) for each multipoint feature.
Is it possible in spatialite?