Table: districts_ap
Columns: code
district
headquarters
population_2011
area_km
density_km
official_website

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 districts_ap WHERE "density_km" > 462 AND "official_website" = 'http://krishna.nic.in/'