CREATE TABLE "past_winners" (
  "year" real,
  "mens_singles" text,
  "womens_singles" text,
  "mens_doubles" text,
  "womens_doubles" text,
  "mixed_doubles" text
);

Question: How many couples won the Mixed Doubles in 1997?
SQL: SELECT COUNT("mixed_doubles") FROM "past_winners" WHERE "year"=1997;