Who was the womens double winner when the womens singles winner was Ding Ning?
CREATE TABLE "slovenian_open" (
  "year_location" text,
  "mens_singles" text,
  "womens_singles" text,
  "mens_doubles" text,
  "womens_doubles" text
);
SELECT "womens_doubles" FROM "slovenian_open" WHERE "womens_singles"='Ding Ning';