What's the average destroyed with a 1990 over 12, more than 1 damaged, 6 survivors, and a to Iran less than 4?
CREATE TABLE "iraqi_air_force_strength_at_start_of_war" (
  "aircraft" text,
  "1990" real,
  "destroyed" real,
  "damaged" real,
  "to_iran" real,
  "survived" real
);
SELECT AVG("destroyed") FROM "iraqi_air_force_strength_at_start_of_war" WHERE "1990">12 AND "damaged">1 AND "to_iran"<4 AND "survived"=6;