What are the smallest assets with a Company of piraeus bank, and a Revenue (US$ billion) smaller than 3.9?
CREATE TABLE "forbes_global_2000" (
  "rank" real,
  "company" text,
  "revenues_us_billion" real,
  "profit_us_billion" real,
  "assets_us_billion" real,
  "market_value_us_billion" real
);
SELECT MIN("assets_us_billion") FROM "forbes_global_2000" WHERE "company"='piraeus bank' AND "revenues_us_billion"<3.9;