What is the rate of drivers completing all the laps in the 2008 Australian Grand Prix?
completing all the laps refers to time is not null; rate = divide(COUNT(raceID where time is not null), COUNT(raceID))
SELECT CAST(SUM(IIF(T1.time IS NOT NULL, 1, 0)) AS REAL) * 100 / COUNT(T1.resultId) FROM results AS T1 INNER JOIN races AS T2 ON T1.raceId = T2.raceId WHERE T2.name = 'Australian GrAND Prix' AND T2.year = 2008