What's the average number of floors that were built in 2004, and have a roof (m) of 106?
CREATE TABLE "completed" (
  "rank" real,
  "city" text,
  "roof_m" real,
  "spire_m" text,
  "floors" real,
  "built" real
);
SELECT AVG("floors") FROM "completed" WHERE "built"=2004 AND "roof_m"=106;