What date was the men's 100m breaststroke in heat 6?
CREATE TABLE "records" (
  "date" text,
  "event" text,
  "heat_semifinal_final" text,
  "nation" text,
  "time" text
);
SELECT "date" FROM "records" WHERE "event"='men''s 100m breaststroke' AND "heat_semifinal_final"='heat 6';