user: Question: Which Surface has a Partner of Oliver Marach?
Columns: ['Outcome', 'Date', 'Surface', 'Partner', 'Opponent in the final', 'Score in the final']
Types: ['text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['Runner-up', '16 July 2006', 'Clay', 'Oliver Marach', 'Jonas Björkman Thomas Johansson', '3–6, 6–4, [4–10]']
SQL:

assistant: SELECT "Surface" FROM "Table" WHERE "Partner" = 'Oliver Marach';