Table: us_house_oh_elections
Columns: district
incumbent
2008_status
democratic
republican

Question: How many districts featured the democrat nicholas von stein?
SQL: SELECT COUNT("district") FROM us_house_oh_elections WHERE "democratic" = 'nicholas von stein'

Question: Which incumbent's democratic candidate was mike carroll?
SQL: SELECT "incumbent" FROM us_house_oh_elections WHERE "democratic" = 'mike carroll'