with union_geom as (
    SELECT ST_Union(ST_Multi(the_geom)) as the_geom
      FROM таблица
     WHERE is_deleted is false
       AND branch_id in (select branch_id from таблица where name in ('Санкт-Петербург','Санкт-Петербург Область'))
    ),
    dump_geom as (
        SELECT (ST_Dump(the_geom)).geom as the_geom
          FROM union_geom
    ),
    simple_geom as (
        SELECT ST_Simplify(ST_SetSRID(ST_MakePolygon(ST_ExteriorRing(the_geom)), 4326), 0.0005) as the_geom
          FROM dump_geom
    )
    SELECT  st_astext(ST_Union(ST_Difference(cast(st_buffer(cast(the_geom as geography), 10000) as geometry), the_geom))) as the_geom  FROM simple_geom