user: Question: What is the date where the attendance was 31,220?
Columns: ['Date', 'Opponent', 'Score', 'Loss', 'Attendance', 'Record']
Types: ['text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['August 1', 'Dodgers', '9–6', 'Thompson (2–2)', '48,071', '49–40']
SQL:

assistant: SELECT "Date" FROM "Table" WHERE "Attendance" = '31,220';