Boundaries Intersections

gis=> select a.osm_id, a."name:en", b.osm_id, b."name:en", round(ST_Area(ST_Intersection(a.way, b.way)::geography)/1000000) as area_km2, ST_AsText(ST_Centroid(ST_Intersection(a.way, b.way))) as center from at_polygon a inner join at_polygon b on a.osm_id != b.osm_id and a.way && b.way where a.admin_level='2' and b.admin_level='2' and a.boundary='administrative' and b.boundary='administrative' and a.osm_id < b.osm_id and b.osm_id < 0 and ST_Intersects(a.way, b.way) order by area_km2 desc limit 20;
  osm_id  |         name:en         |  osm_id  |         name:en          | area_km2 |                   center
----------+-------------------------+----------+--------------------------+----------+--------------------------------------------
   -60199 | Ukraine                 |   -60189 | Russia                   |    44799 | POINT(34.3620300516289 45.2171795055881)
 -1656678 | South Sudan             |  -192789 | Sudan                    |    23147 | POINT(26.050412528483 9.48777979190103)
  -307829 | Haiti                   |  -148838 | United States of America |     1746 | POINT(-75.0137486468775 18.4028571650422)
  -286393 | Argentina               |  -167454 | Chile                    |     1507 | POINT(-73.2951125519333 -49.4915930163872)
 -1428125 | Canada                  |  -148838 | United States of America |      578 | POINT(-67.1371505877121 44.459808705718)
  -449220 | Taiwan                  |  -270056 | China                    |      407 | POINT(119.993523485709 26.2081430743007)
  -449220 | Taiwan                  |  -270056 | China                    |      277 | POINT(118.351311662216 24.4426029867618)
 -2323309 | The Netherlands         |   -51477 | Germany                  |      264 | POINT(6.71178441000846 53.5108114523677)
 -1428125 | Canada                  |  -148838 | United States of America |      109 | POINT(-140.919706509331 69.7748777281029)
 -1741311 | Serbia                  |  -214885 | Croatia                  |       99 | POINT(18.9058620655204 45.7703427407642)
  -449220 | Taiwan                  |  -270056 | China                    |       90 | POINT(119.965674546357 25.9662536685956)
 -1703814 | Palestinian Territories | -1473946 | Israel                   |       70 | POINT(35.2246457423727 31.7840924565514)
  -449220 | Taiwan                  |  -270056 | China                    |       53 | POINT(120.226351993941 26.3394680962033)
  -449220 | Taiwan                  |  -270056 | China                    |       52 | POINT(120.488227295244 26.3688691722675)
  -218657 | Slovenia                |  -214885 | Croatia                  |       45 | POINT(13.4763409023349 45.5471286535986)
  -449220 | Taiwan                  |  -270056 | China                    |       19 | POINT(119.462511680242 24.9902599054372)
 -2171347 | Luxembourg              |   -51477 | Germany                  |        7 | POINT(6.37445942266256 49.7263622848021)
  -252645 | Bolivia                 |   -59470 | Brazil                   |        5 | POINT(-65.3571669145145 -10.7930812644583)
  -443174 | Philippines             |  -270056 | China                    |        2 | POINT(114.112730361287 10.9441562730741)
 -2202162 | France                  |  -365331 | Italy                    |        1 | POINT(6.86265648948385 45.8332959568394)