How many jockeys are listed running at the Sir Rupert Clarke Stakes?
CREATE TABLE "2006_07_season_as_a_five_year_old" (
  "result" text,
  "date" text,
  "race" text,
  "venue" text,
  "group" text,
  "distance" text,
  "weight_kg" text,
  "jockey" text,
  "winner_2nd" text
);
SELECT COUNT("jockey") FROM "2006_07_season_as_a_five_year_old" WHERE "race"='Sir Rupert Clarke Stakes';