What's the average year for the name aida-wedo dorsa with a diameter less than 450?
CREATE TABLE "dorsa" (
  "name" text,
  "latitude" text,
  "longitude" text,
  "diameter_km" real,
  "year_named" real
);
SELECT AVG("year_named") FROM "dorsa" WHERE "name"='aida-wedo dorsa' AND "diameter_km"<450;