How many players are there for mens singles when chen qi ma lin played mens doubles?
CREATE TABLE "japan_open" (
  "year_location" text,
  "mens_singles" text,
  "womens_singles" text,
  "mens_doubles" text,
  "womens_doubles" text
);
SELECT COUNT("mens_singles") FROM "japan_open" WHERE "mens_doubles"='Chen Qi Ma Lin';