Who is the mens singles and womens singlses is wang shixian?
CREATE TABLE "previous_winners" (
  "year" real,
  "mens_singles" text,
  "womens_singles" text,
  "mens_doubles" text,
  "womens_doubles" text,
  "mixed_doubles" text
);
SELECT "mens_singles" FROM "previous_winners" WHERE "womens_singles"='Wang Shixian';