What shows for round when the race was Int. Adac Preis Von Zweibrücken?
CREATE TABLE "race_calendar_and_winners" (
  "round" real,
  "race" text,
  "circuit" text,
  "date" text,
  "event" text,
  "winning_driver" text
);
SELECT "round" FROM "race_calendar_and_winners" WHERE "race"='int. adac preis von zweibrücken';