Score F–A of 2–0, and a Opponents of walsall has what date?
CREATE TABLE "pre_season_friendles" (
  "date" text,
  "opponents" text,
  "venue" text,
  "result" text,
  "score_f_a" text
);
SELECT "date" FROM "pre_season_friendles" WHERE "score_f_a"='2–0' AND "opponents"='walsall';