user: Question: How many years have an Opponent in the final of Welby Van Horn?
Columns: ['Outcome', 'Year', 'Championship', 'Surface', 'Opponent in the final', 'Score in the final']
Types: ['text', 'real', 'text', 'text', 'text', 'text']
Sample row: ['Runner-up', 1939.0, 'French Championships', 'Clay', 'Don McNeill', '5–7, 0–6, 3–6']
SQL:

assistant: SELECT COUNT("Year") FROM "Table" WHERE "Opponent in the final" = 'Welby Van Horn';