What is the oldest model Porsche v12 that has points less than or equal to 0.
CREATE TABLE "complete_formula_one_world_championship_" (
  "year" real,
  "entrant" text,
  "chassis" text,
  "engine" text,
  "pts" real
);
SELECT MIN("year") FROM "complete_formula_one_world_championship_" WHERE "engine"='porsche v12' AND "pts"<0;