What is the average number of golds for teams in rank 17 with more than 4 silver?
CREATE TABLE "medal_table" (
  "rank" text,
  "nation" text,
  "gold" real,
  "silver" real,
  "bronze" real,
  "total" real
);
SELECT AVG("gold") FROM "medal_table" WHERE "rank"='17' AND "silver">4;