Table schema:
CREATE TABLE table_name_4 (laps INTEGER, grid VARCHAR, manufacturer VARCHAR, time_retired VARCHAR)

Question: 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?
SQL: SELECT MIN(laps) FROM table_name_4 WHERE manufacturer = "yamaha" AND time_retired = "+1:08.312" AND grid < 20