user: Question: When was the Austrian Grand Prix?
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', '12 April', 'Jacarepaguá', 'Nigel Mansell', 'Nelson Piquet', 'Alain Prost', 'McLaren - TAG', 'Report']
SQL:

assistant: SELECT "Date" FROM "Table" WHERE "Grand Prix" = 'Austrian Grand Prix';