user: Question: Name the incumbent for Virginia 18
Columns: ['District', 'Incumbent', 'Party', 'First elected', 'Result', 'Candidates']
Types: ['text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['Virginia 1', 'John G. Jackson', 'Democratic-Republican', '1803', 'Re-elected', 'John G. Jackson (DR) 57.2% Thomas Wilson (F) 42.8%']
SQL:

assistant: SELECT "Incumbent" FROM "Table" WHERE "District" = 'Virginia 18';