user: Question: what is the earliest began when the court surface is Clay in Hamburg?
Columns: ['Tournament', 'Country', 'Location', 'Began', 'Court surface']
Types: ['text', 'text', 'text', 'real', 'text']
Sample row: ['Indian Wells Masters', 'United States', 'Indian Wells', 1974.0, 'Hard']
SQL:

assistant: SELECT MIN("Began") FROM "Table" WHERE "Court surface" = 'Clay' AND "Location" = 'Hamburg';