user: Question: How many winners have a runner-up of A. Karthikeyan?
Columns: ['Constituency', 'Winner', 'Party', 'Margin', 'Runner-up a', 'Party a']
Types: ['text', 'text', 'text', 'real', 'text', 'text']
Sample row: ['Madras North', 'D. Pandian', 'INC', 113771.0, 'N. V. N. Somu', 'DMK']
SQL:

assistant: SELECT COUNT("Winner") FROM "Table" WHERE "Runner-up a" = 'A. Karthikeyan';