user: Question: Which winning driver of the Roussillon Grand Prix had an Alfa Romeo?
Columns: ['Name', 'Circuit', 'Date', 'Winning driver', 'Winning constructor', 'Report']
Types: ['text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['Nice Grand Prix', 'Nice', '22 April', 'Luigi Villoresi', 'Maserati', 'Report']
SQL:

assistant: SELECT "Winning driver" FROM "Table" WHERE "Winning constructor" = 'Alfa Romeo' AND "Name" = 'Roussillon Grand Prix';