user: Question: What was the date of Circuit Hockenheimring and the winning manufacturer being Mercedes-Benz?
Columns: ['Round', 'Circuit', 'Date', 'Fastest lap', 'Winning driver', 'Winning team', 'Winning manufacturer']
Types: ['real', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: [1.0, 'Hockenheimring', '28 May', 'Bernd Schneider', 'Bernd Schneider', 'HWA 1', 'Mercedes-Benz']
SQL:

assistant: SELECT "Date" FROM "Table" WHERE "Circuit" = 'Hockenheimring' AND "Winning manufacturer" = 'Mercedes-Benz';