What is the Date of the match with a Score in the final of 6–3, 6–3, 2–6, 6–4?
CREATE TABLE "singles_18_12_6" (
  "outcome" text,
  "date" text,
  "championship" text,
  "surface" text,
  "opponent_in_the_final" text,
  "score_in_the_final" text
);
SELECT "date" FROM "singles_18_12_6" WHERE "score_in_the_final"='6–3, 6–3, 2–6, 6–4';