user: Question: On what date was the winning score –20 (68-67-65-64=264)?
Columns: ['Date', 'Tournament', 'Winning score', 'Margin of victory', 'Runner(s) up']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['Jul 13, 1997', 'Quad City Classic', '–15 (67-66-67-65=265)', '3 strokes', 'Brandel Chamblee']
SQL:

assistant: SELECT "Date" FROM "Table" WHERE "Winning score" = '–20 (68-67-65-64=264)';