What is the average total for the Men's Open of 7, and the men's wheelchair more than 0?
CREATE TABLE "victories_by_nationality" (
  "country" text,
  "men_s_open" real,
  "women_s_open" real,
  "men_s_wheelchair" real,
  "women_s_wheelchair" real,
  "total" real
);
SELECT AVG("total") FROM "victories_by_nationality" WHERE "men_s_open"=7 AND "men_s_wheelchair">0;