what is the date when the surface is clay and the result is 6–7 (4–7) , 1–6?
CREATE TABLE "singles_15" (
  "edition" text,
  "round" text,
  "date" text,
  "against" text,
  "surface" text,
  "opponent" text,
  "result" text
);
SELECT "date" FROM "singles_15" WHERE "surface"='clay' AND "result"='6–7 (4–7) , 1–6';