psql -d osm -c  "select members from planet_osm_rels\
                     where hstore(tags)->'name'='Corneilla-la-Rivière';"
                               members
----------------------------------------------------------------------------
{w121772197,outer,w100006391,outer,w121772204,outer,n287557758,admin_centre}

CREATE OR REPLACE FUNCTION admin_centre(anyarray)
   RETURNS bigint
   LANGUAGE sql
   AS $function$
      SELECT cast(substring($1[i] from 2) as bigint)
         FROM generate_series(array_lower($1,1),array_upper($1,1),2) i 
         WHERE $1[i+1]='admin_centre';$function$

select poly.name, point.name, point."name:ca", point.population 
   from planet_osm_rels r, 
        planet_osm_polygon poly, 
        planet_osm_point point 
   where poly.admin_level='8' 
         and admin_centre(r.members) = point.osm_id 
         and r.id = -poly.osm_id ;

create table admin_rel 
   as select -id as rel_id,
             admin_centre(members) as admin_centre
        from planet_osm_rels 
        where hstore(tags)->'boundary'='administrative' and 
              hstore(tags)->'admin_level'  in ('8','6','4');

/*
  Osmium Javascript Example:  shape_export.js

  run with: osmjs -2 -m -l sparsetable -j shape_export.js OSMFILE
*/

var shp_places = Osmium.Output.Shapefile.open('./places', 'point');
shp_places.add_field('id', 'string', 12);
shp_places.add_field('type', 'string', 32);
shp_places.add_field('name', 'string', 32);

var shp_boundaries = Osmium.Output.Shapefile.open('./boundaries', 'polygon');
shp_boundaries.add_field('id', 'integer', 10);
shp_boundaries.add_field('type', 'string', 32);
shp_boundaries.add_field('boundary', 'string', 255);
shp_boundaries.add_field('admin_level', 'string', 255);

var csv_file = Osmium.Output.CSV.open("./rels.csv");

var node_tags = {
    place: { village: 'villaget', city: 'city', town: 'town'} //,
    //shop: { supermarket: 'supermarket' }
}

Osmium.Callbacks.init = function() {
    print("Init");
}
Osmium.Callbacks.node = function() {
    for (var key in this.tags) {
        if (node_tags[key]) {
            var type = node_tags[key][this.tags[key]];
            if (type) {
                shp_places.add(this.geom, { id: this.id, type: type, name: this.tags.name });
            }
        }
    }
}
Osmium.Callbacks.area = function() {
    if (this.tags.boundary) {
        shp_boundaries.add(this.geom, { id: this.id, type: this.tags.boundary, admin_level: this.tags.admin_level});
    }
}
Osmium.Callbacks.relation = function() {
   for (var key in this.members) {
      for (var key2 in this.members[key]) {
         if (key2=='role' && this.members[key].role=='admin_centre'){
            csv_file.print(this.id*2+1, this.members[key].ref, 
                           this.members[key].role, this.members[key].type);
         }
      }
   }
}
Osmium.Callbacks.end = function() {
    shp_places.close();
    shp_boundaries.close();
    csv_file.close();
    print("Done");
}