How much silver does the rank have that has gold smaller than 4, and a total of 1 and a rank larger than 6?
CREATE TABLE "performances_by_nation" (
  "rank" real,
  "gold" real,
  "silver" real,
  "bronze" real,
  "total" real
);
SELECT SUM("silver") FROM "performances_by_nation" WHERE "gold"<4 AND "total"=1 AND "rank">6;