CREATE TABLE table_name_28 (date VARCHAR, competition VARCHAR, opponents VARCHAR)

What is Date, when Competition is 'F', and when Opponents is 'FC Astoria Walldorf'?
SELECT date FROM table_name_28 WHERE competition = "f" AND opponents = "fc astoria walldorf"
SELECT "date" FROM "table_name_28" WHERE "competition" = "f" AND "fc astoria walldorf" = "opponents"