user: Question: who is the the opponent with district being Ohio12
Columns: ['District', 'Incumbent', 'Party', 'First elected', 'Status', 'Opponent']
Types: ['text', 'text', 'text', 'real', 'text', 'text']
Sample row: ['Ohio1', 'David S. Mann', 'Democratic', 1992.0, 'Defeated Republican gain', 'Steve Chabot (R) 56.1% David S. Mann (D) 43.9%']
SQL:

assistant: SELECT "Opponent" FROM "Table" WHERE "District" = 'Ohio12';