What was the surface on 23 October 2011?
CREATE TABLE "singles_5_1_4" (
  "outcome" text,
  "date" text,
  "surface" text,
  "opponent_in_the_final" text,
  "score_in_the_final" text
);
SELECT "surface" FROM "singles_5_1_4" WHERE "date"='23 october 2011';