question: What is the highest Laps, when Bike is "Yamaha YZF-R1", when Rider is "David Checa", and when Grid is greater than 18?
answer: SELECT MAX(laps) FROM table_name_78 WHERE bike = "yamaha yzf-r1" AND rider = "david checa" AND grid > 18
context: CREATE TABLE table_name_78 (laps INTEGER, grid VARCHAR, bike VARCHAR, rider VARCHAR)