Name the average goal difference for draw of 7 and played more than 18
CREATE TABLE "final_league_position" (
  "team" text,
  "played" real,
  "draw" real,
  "lost" real,
  "goals_for" real,
  "goals_against" real,
  "goal_difference" real,
  "points" real
);
SELECT AVG("goal_difference") FROM "final_league_position" WHERE "draw"=7 AND "played">18;