Dissolve keeping all attributes values (concatenation/aggregation)?

[celati Laurent]

Dear all,

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/
<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*

Thanks so much
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