What was the date of Circuit Hockenheimring and the winning manufacturer being Mercedes-Benz?
CREATE TABLE "race_calendar_and_winners" (
  "round" real,
  "circuit" text,
  "date" text,
  "fastest_lap" text,
  "winning_driver" text,
  "winning_team" text,
  "winning_manufacturer" text
);
SELECT "date" FROM "race_calendar_and_winners" WHERE "circuit"='hockenheimring' AND "winning_manufacturer"='mercedes-benz';