Dissolve keeping all attributes values (concatenation/aggregation)?

[celati Laurent]

Dear Erik,
Thank you.
But when i rerun the query with the edit (adding the closing parenthesis) :











*SELECT     min(union_v4.max_hierar) as id,     array_agg(union_v4.id
<http://union_v4.id>) as ids,     union_v6.geomFROM union_v4,    (SELECT
      (ST_Dump(St_multi(ST_Union(geom)))).geom as geom    FROM
union_v6)WHERE     st_intersects(union_v4.geom, union_v6.geom)GROUP BY
union_v6.geom*



*I obtain this time the message : * ERROR: la relation « union_v4 »
n'existe pas LINE 5: FROM union_v4, ^ ERREUR: la relation « union_v4 »
n'existe pas SQL state: 42P01 Character: 105


However, i have one table called "union_v4" within my postgis db.
thanks so much.


Le mar. 30 sept. 2025 à 17:04, Erik Wienhold <ewie at ewie.name> a écrit :

> On 2025-09-30 16:08 +0200, celati Laurent wrote:
> > I work with qgis and postgis. I would like to perform a "dissolve":
> >
> https://docs.qgis.org/3.40/en/docs/user_manual/processing_algs/qgis/vectorgeometry.html#dissolve
> >
> > in keeping/preserving  all attributes values ? For instance : a kind of
> > aggregation/concatenation within new "output features" ?
> >
> > I Saw this post :
> >
> https://www.aproposinfosystems.com/en/about/blog/managing-attributes-postgis-dissolve/
> >
> > I have tried to reproduce the proposal with my postgis table containing
> > several polygons
> >
> > *SELECT min(union_v4.max_hierar) as id, array_agg(union_v4.id
> > <http://union_v4.id>) as ids, union_v6.geomFROM union_v4, (SELECT
> > (ST_Dump(St_multi(ST_Union(geom)))).geom as geom FROM union_v6WHERE
> > st_intersects(union_v4.geom, union_v6.geom)GROUP BY union_v6.geom*
> >
> > But i obtain :
> >
> > *ERROR: syntax error at the end of the entryLINE 12: GROUP BY
> union_v6.geom
> > ^ERROR: syntax error at the end of the entrySQL state: 42601Characters:
> 285*
>
> Your query is missing the closing parenthesis of the union_v6 subquery
> (after "FROM union_v6").  This should work:
>
>         SELECT
>             min(union_v4.max_hierar) as id,
>             array_agg(union_v4.id) as ids,
>             union_v6.geom
>         FROM union_v4,
>             (SELECT
>                 (ST_Dump(St_multi(ST_Union(geom)))).geom as geom
>             FROM union_v6) union_v6
>         WHERE st_intersects(union_v4.geom, union_v6.geom)
>         GROUP BY union_v6.geom;
>
> --
> Erik Wienhold
>
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