Who was the jockey at Rosehill and the weight was 57.5 kg?
CREATE TABLE "2002_03_season_as_a_four_year_old" (
  "result" text,
  "date" text,
  "race" text,
  "venue" text,
  "group" text,
  "distance" text,
  "weight_kg" text,
  "time" text,
  "jockey" text,
  "winner_2nd" text
);
SELECT "jockey" FROM "2002_03_season_as_a_four_year_old" WHERE "venue"='Rosehill' AND "weight_kg"='57.5';