What's the total number of floors built after 2006, and have a rank of 12?
CREATE TABLE "completed" (
  "rank" real,
  "city" text,
  "roof_m" real,
  "spire_m" text,
  "floors" real,
  "built" real
);
SELECT SUM("floors") FROM "completed" WHERE "built">2006 AND "rank"=12;