What is the total number of gold medals won by nations that won 2 silver medals but fewer than 7 in total?
CREATE TABLE "performance_by_nation" (
  "rank" text,
  "gold" real,
  "silver" real,
  "bronze" real,
  "total" real
);
SELECT SUM("gold") FROM "performance_by_nation" WHERE "silver"=2 AND "total"<7;