What is the sum of the difference for 9 draws and over 18 played?
CREATE TABLE "torneo_apertura_opening_tournament" (
  "team" text,
  "points" real,
  "played" real,
  "drawn" real,
  "lost" real,
  "against" real,
  "diff" real
);
SELECT SUM("diff") FROM "torneo_apertura_opening_tournament" WHERE "drawn"=9 AND "played">18;