The asker did not ask for a generic method. If they had then the question would not be too broad, but it should be responded to with generic methods and not specific procedures. In this case the question seemed to be asking for a specific procedure in any (of many) open source GIS products. Enabling both questions to stay open and answered via editing Q&As is I think a good result.
If the askers were not satisfied with either of the two answers, then there is always the opportunity to ask another question that starts by explaining why when they want a solution in any open source GIS the QGIS and PostGIS answers did not meet their requirements.
