When the # is 4, what is the pop./ km²?
CREATE TABLE "overview_of_the_regions" (
  "num" real,
  "name" text,
  "name_english" text,
  "population_2008_07_01" real,
  "area_km" real,
  "pop_km" text,
  "iso_3166_2" text,
  "administrative_centre" text
);
SELECT "pop_km" FROM "overview_of_the_regions" WHERE "num"=4;