who is the the mens doubles with mens singles being jürgen koch and womens singles being sabine ploner
CREATE TABLE "past_winners" (
  "year" real,
  "mens_singles" text,
  "womens_singles" text,
  "mens_doubles" text,
  "womens_doubles" text,
  "mixed_doubles" text
);
SELECT "mens_doubles" FROM "past_winners" WHERE "mens_singles"='Jürgen Koch' AND "womens_singles"='Sabine Ploner';