user: Question: Which Conference Joined has a Previous Conference of Northwestern, and a Mascot of Oilers?
Columns: ['School', 'Location', 'Mascot', 'County', 'Year Joined', 'Previous Conference', 'Year Left', 'Conference Joined']
Types: ['text', 'text', 'text', 'text', 'real', 'text', 'real', 'text']
Sample row: ['Hammond Clark', 'Hammond', 'Pioneers', '45 Lake', 1969.0, 'Northwestern', 2007.0, 'Great Lakes']
SQL:

assistant: SELECT "Conference Joined" FROM "Table" WHERE "Previous Conference" = 'Northwestern' AND "Mascot" = 'Oilers';