user: Question: What is the average Year, when Outcome is "Winner"?
Columns: ['Outcome', 'Year', 'Pro Slam Championship', 'Surface', 'Opponent in the final', 'Score in the final']
Types: ['text', 'real', 'text', 'text', 'text', 'text']
Sample row: ['Runner-up', 1942.0, 'US Pro', 'Grass', 'Don Budge', '2–6, 2–6, 2–6']
SQL:

assistant: SELECT AVG("Year") FROM "Table" WHERE "Outcome" = 'Winner';