Table: race_results_49
Columns: rider
manufacturer
laps
time_retired
grid

Question: What time/retired for a grid less than 19, under 21 laps, and made by aprilia?
SQL: SELECT "time_retired" FROM race_results_49 WHERE "grid" < 19 AND "manufacturer" = 'aprilia' AND "laps" < 21

Question: What is the grid for dirk heidolf?
SQL: SELECT SUM("grid") FROM race_results_49 WHERE "rider" = 'dirk heidolf'