WHat is the number of Population has a Density of 50.09 and a Rank larger than 30?
CREATE TABLE "by_population" (
  "rank" real,
  "province" text,
  "population" real,
  "area" real,
  "density" real
);
SELECT SUM("population") FROM "by_population" WHERE "density"=50.09 AND "rank">30;