CREATE TABLE "21st_century" (
  "year" real,
  "men_s_singles" text,
  "women_s_singles" text,
  "men_s_doubles" text,
  "women_s_doubles" text,
  "mixed_doubles" text
);

Question: What players played mixed doubles when zhang xi played mixed singles?
SQL: SELECT "mixed_doubles" FROM "21st_century" WHERE "women_s_singles"='zhang xi';

Question: What player played women's singles when marcus ellis heather olver played mixed doubles?
SQL: SELECT "women_s_singles" FROM "21st_century" WHERE "mixed_doubles"='marcus ellis heather olver';

Question: What player played women's doubles when lee jae-jin lee eun-woo played mixed doubles?
SQL: SELECT "women_s_doubles" FROM "21st_century" WHERE "mixed_doubles"='lee jae-jin lee eun-woo';

Question: What year did helle nielsen marie røpke play womens' doubles?
SQL: SELECT "year" FROM "21st_century" WHERE "women_s_doubles"='helle nielsen marie røpke';

Question: What is the latest year that chou tien-chen played men's singles?
SQL: SELECT MAX("year") FROM "21st_century" WHERE "men_s_singles"='chou tien-chen';