What is Date, when Competition is "F", and when Opponents is "FC Astoria Walldorf"?
CREATE TABLE "results" (
  "date" text,
  "venue" text,
  "opponents" text,
  "score" text,
  "competition" text,
  "match_report" text
);
SELECT "date" FROM "results" WHERE "competition"='f' AND "opponents"='fc astoria walldorf';