I have a shapefile with lots of polygons and I need to union all polygons which have the same identifier-id into a new (multi-)polygon, ideally with the same identifier-id on another (new) layer.
As there are lots of polygons I don't want to do this manually. Is there a simple way I can do this automatically in QGIS? I suppose This can be done with Spatialite, but that's only a guess.
Please help a rookie. Any hints appreciated. Thank you!