user: Question: how many winners were in round 8
Columns: ['Rd', 'Race', 'Pole Position', 'Fastest Lap', 'Winning driver', 'Winning team', 'Report']
Types: ['real', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: [2.0, 'Monterey Festival of Speed', 'James Hinchcliffe', 'Douglas Soares', 'James Hinchcliffe', 'Forsythe Pettit Racing', 'Report']
SQL:

assistant: SELECT COUNT("Winning driver") FROM "Table" WHERE "Rd" = 8.0;