user: Question: Which Date has a MotoGP winner of Casey Stoner, and a 250cc winner of Hiroshi Aoyama?
Columns: ['Round', 'Date', 'Grand Prix', 'Circuit', '125cc winner', '250cc winner', 'MotoGP winner', 'Report']
Types: ['real', 'text', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: [1.0, '12–13 April', 'Qatar Grand Prix ‡', 'Losail', 'Andrea Iannone', 'Héctor Barberá', 'Casey Stoner', 'Report']
SQL:

assistant: SELECT "Date" FROM "Table" WHERE "MotoGP winner" = 'Casey Stoner' AND "250cc winner" = 'Hiroshi Aoyama';