What is the Men's Open when the venue is Perth?
CREATE TABLE "results_of_the_national_championships_19" (
  "year" real,
  "venue" text,
  "men_s_open" text,
  "women_s_open" text,
  "men_s_35s" text
);
SELECT "men_s_open" FROM "results_of_the_national_championships_19" WHERE "venue"='perth';