user: Question: What is Surface, when Championship is Australian Open?
Columns: ['Outcome', 'Year', 'Championship', 'Surface', 'Opponent', 'Score']
Types: ['text', 'real', 'text', 'text', 'text', 'text']
Sample row: ['Winner', 1999.0, 'US Open', 'Hard', 'Martina Hingis', '6–3, 7–6 (7–4)']
SQL:

assistant: SELECT "Surface" FROM "Table" WHERE "Championship" = 'Australian Open';