user: Question: What is the surface at the tournament of Vaihingen?
Columns: ['Date', 'Tournament', 'Surface', 'Opponent in the final', 'Score']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['20 May 1990', 'Bournemouth', 'Clay', 'Anna Benzon', '7–6, 6–1']
SQL:

assistant: SELECT "Surface" FROM "Table" WHERE "Tournament" = 'Vaihingen';