user: Question: On what surface was the Australian Open (6) played on?
Columns: ['Outcome', 'Year', 'Championship', 'Surface', 'Partner', 'Opponents', 'Score']
Types: ['text', 'real', 'text', 'text', 'text', 'text', 'text']
Sample row: ['Winner', 2003.0, 'French Open', 'Clay', 'Mike Bryan', 'Paul Haarhuis Yevgeny Kafelnikov', '7–6 (7–3) , 6–3']
SQL:

assistant: SELECT "Surface" FROM "Table" WHERE "Championship" = 'Australian Open (6)';