user: Question: What is the highest Laps, when Bike is "yamaha yzf-r1", when Rider is "david checa", and when Grid is greater than 18?
Columns: ['Rider', 'Bike', 'Laps', 'Time', 'Grid']
Types: ['text', 'text', 'real', 'text', 'real']
Sample row: ['Ruben Xaus', 'Ducati 1098 RS 08', 24.0, '39:19.710', 3.0]
SQL:

assistant: SELECT MAX("Laps") FROM "Table" WHERE "Bike" = 'yamaha yzf-r1' AND "Rider" = 'david checa' AND "Grid" > 18.0;