user: Question: What is the earliest Date on a Surface of clay in a Championship in linz, austria?
Columns: ['Outcome', 'Date', 'Championship', 'Surface', 'Opponent in the final', 'Score in the final']
Types: ['text', 'real', 'text', 'text', 'text', 'text']
Sample row: ['Runner-up', 1975.0, 'Båstad , Sweden', 'Clay', 'Manuel Orantes', '0–6, 3–6']
SQL:

assistant: SELECT MIN("Date") FROM "Table" WHERE "Surface" = 'clay' AND "Championship" = 'linz, austria';