I have got two geometries one is polygons (postcode boundaries) and second is linestring (roads). I want to intersect them together and want roads that are intersecting the polygons. While doing this I got that many sections of roads are still connected to each other (dissolved). So I want to separate them (explode) as they are in geometry. I did search for the solution but haven't found anything.

This is the case below they all are a one feature in QGIS. I want them as single entity.

enter image description here

1 Answer 1


You can use st_dump() to transform multi-parts to single-parts

SELECT sometable.field1, sometable.field2,
      (ST_Dump(sometable.the_geom)).geom AS the_geom
FROM sometable;
  • Thanks for that. But I have run this query. Result is not just satisfactory, Still the same problem.
    – Sri
    Jan 9, 2020 at 12:41
  • @Shobhit what do you mean? st_dump is the tool to explode a multi-part to single parts, which is what you have asked... Clarify the question if you want something else
    – JGH
    Jan 9, 2020 at 12:46
  • Sorry for any confusion. Like in the photo uploaded their are three links which have a common field i.e. RoadName. I have clipped this Road data with post code boundary but the road segments are still connected due the same name. So I just simply want to separate them as single feature. So that if you select a feature that will show you just one feature not others.
    – Sri
    Jan 9, 2020 at 13:22
  • @Shobhit and what is wrong with applying st_dump on the clip output?
    – JGH
    Jan 9, 2020 at 14:48
  • It is actually not exploding the geometries. So I have run another method, ST_Union, ST_Multi and then ST_Dump. Because it was not exploding so Merged them then break all of them. I am pretty sure there would be another better method but it worked for me. SELECT sometable.field1, sometable.field2, (ST_Dump(St_multi(ST_Union(sometable.the_geom)))).geom AS the_geom FROM sometable Group By sometable.field1, sometable.field2,; Thanks JGH at least you came forward for help. :)
    – Sri
    Jan 10, 2020 at 10:35

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