How many times did  li ju win the womens singles and wang liqin win the mens singles?
CREATE TABLE "china_open" (
  "year_location" text,
  "mens_singles" text,
  "womens_singles" text,
  "mens_doubles" text,
  "womens_doubles" text
);
SELECT COUNT("womens_doubles") FROM "china_open" WHERE "womens_singles"='Li Ju' AND "mens_singles"='Wang Liqin';