user: Question: On what Date was Rafael Nadal the Opponent?
Columns: ['Date', 'Tournament', 'Surface', 'Opponent', 'Score']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['10 August 1998', 'San Marino', 'Clay', 'Mariano Puerta', '6–2, 7–5']
SQL:

assistant: SELECT "Date" FROM "Table" WHERE "Opponent" = 'Rafael Nadal';