What was the minimum population in 2011 of the district of Prakasam?
CREATE TABLE "external_links" (
  "code" text,
  "district" text,
  "headquarters" text,
  "population_2011" real,
  "area_km" real,
  "density_km" real,
  "official_website" text
);
SELECT MIN("population_2011") FROM "external_links" WHERE "district"='Prakasam';