What is the average number of points of the team with more than 17 pg won?
CREATE TABLE "anaprof_2008_relegation_table" (
  "place_posici_n" real,
  "team_equipo" text,
  "played_pj" real,
  "won_pg" real,
  "draw_pe" real,
  "lost_pp" real,
  "goals_scored_gf" real,
  "goals_conceded_gc" real,
  "dif" real,
  "points_pts" real
);
SELECT AVG("points_pts") FROM "anaprof_2008_relegation_table" WHERE "won_pg">17;