user: Question: Which race had a distance of 4 miles where the runner-up was not known?
Columns: ['Race name', 'Dist (miles)', 'Course', 'Prize', 'Odds', 'Runners', 'Place', 'Runner-up']
Types: ['text', 'text', 'text', 'text', 'text', 'real', 'real', 'text']
Sample row: ['Match race v. Speedwell', '4', 'Newmarket', '500 guineas', 'not known', 2.0, 1.0, 'Speedwell']
SQL:

assistant: SELECT "Race name" FROM "Table" WHERE "Dist (miles)" = '4' AND "Runner-up" = 'not known';