CREATE TABLE "external_links" (
  "code" text,
  "district" text,
  "headquarters" text,
  "population_2011" real,
  "area_km" real,
  "density_km" real,
  "official_website" text
);

Question: What is the sum of the area values for districts having density over 462 and websites of http://krishna.nic.in/?
SQL: SELECT SUM("area_km") FROM "external_links" WHERE "density_km">462 AND "official_website"='http://krishna.nic.in/';