user: Question: What is the margin when Periyakulam is the constituency?
Columns: ['Constituency', 'Winner', 'Party', 'Margin', 'Runner-up a', 'Party a']
Types: ['text', 'text', 'text', 'real', 'text', 'text']
Sample row: ['Madras North', 'Krishnan Manoharan', 'DMK', 51594.0, 'S. G. Vinayaga Moorthy', 'NCO']
SQL:

assistant: SELECT "Margin" FROM "Table" WHERE "Constituency" = 'Periyakulam';