What was the surface for the May 10, 2009 tournament?
CREATE TABLE "atp_challenger_tour_and_itf_futures_doub" (
  "date" text,
  "tournament" text,
  "surface" text,
  "partner" text,
  "opponents" text,
  "score" text
);
SELECT "surface" FROM "atp_challenger_tour_and_itf_futures_doub" WHERE "date"='may 10, 2009';