I have a multi polygon with spatial field layer with and 3000 records and I want to use dissolve all in 1 record.

On DISSOLVE algorithm in QGIS you have a choose to dissolve all features from layer that I want with PostGIS.

After the query I want to have one record and this record have all.

I test this query :

SELECT (ST_Dump(ST_union(geom))).geom::geometry(POLYGON,2100) FROM public.parcel1

but don't work; don't create me one record with all features.

What have I done wrong?

  • 3
    select st_union(geom) geom from parcel1
    – ziggy
    Sep 23, 2017 at 15:02
  • 2
    the query you have is breaking up the spatial table into many singlepart features
    – ziggy
    Sep 23, 2017 at 15:02
  • @Ziggy that export if I use your details is multipolygon or polygon ? Sep 23, 2017 at 15:41
  • "that export"? dont know what you are talking about. it will be a multipolygon
    – ziggy
    Sep 23, 2017 at 16:13

1 Answer 1


To condense all the geometries in a table to one single geometry, you can pass an array to ST_Union:

  • 1
    ST_Union has an aggregate function variant, so you should just be able to use SELECT ST_Union(geom) FROM tbl
    – dr_jts
    Jul 6, 2020 at 21:37
  • @dr_jts that's what we use Jul 7, 2020 at 1:33

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