user: Question: Who had the fastest lap of the race that Ayrton Senna won on 23 April?
Columns: ['Grand Prix', 'Date', 'Location', 'Pole Position', 'Fastest Lap', 'Winning Driver', 'Constructor', 'Report']
Types: ['text', 'text', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['Brazilian Grand Prix', '26 March', 'Jacarepaguá', 'Ayrton Senna', 'Riccardo Patrese', 'Nigel Mansell', 'Ferrari', 'Report']
SQL:

assistant: SELECT "Fastest Lap" FROM "Table" WHERE "Winning Driver" = 'Ayrton Senna' AND "Date" = '23 April';