What is the lowest laps that has a manufacturer of yamaha, and a time/retired of +1:08.312, and a grid less than 20?
CREATE TABLE "moto_gp_classification" (
  "rider" text,
  "manufacturer" text,
  "laps" real,
  "time_retired" text,
  "grid" real
);
SELECT MIN("laps") FROM "moto_gp_classification" WHERE "manufacturer"='yamaha' AND "time_retired"='+1:08.312' AND "grid"<20;