What is the least amount of silver medals won by Total with more than 1 bronze and more than 18 total medals won?
CREATE TABLE "medal_table" (
  "rank" text,
  "nation" text,
  "gold" real,
  "silver" real,
  "bronze" real,
  "total" real
);
SELECT MIN("silver") FROM "medal_table" WHERE "bronze">1 AND "nation"='total' AND "total">18;