user: Question: What date did Mike Rockenfeller have the fastest lap?
Columns: ['Round', 'Circuit', 'Date', 'Pole position', 'Fastest lap', 'Winning driver', 'Winning team']
Types: ['real', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: [1.0, 'Hockenheimring', '25 April', 'Gary Paffett', 'Bruno Spengler', 'Gary Paffett', 'HWA Team']
SQL:

assistant: SELECT "Date" FROM "Table" WHERE "Fastest lap" = 'Mike Rockenfeller';