What is the average number of points for a team in the 250cc class with fewer than 0 wins?
CREATE TABLE "motorcycle_grand_prix_results" (
  "year" real,
  "class" text,
  "team" text,
  "points" real,
  "rank" text,
  "wins" real
);
SELECT AVG("points") FROM "motorcycle_grand_prix_results" WHERE "class"='250cc' AND "wins"<0;