user: Question: What is the year that the Roughriders left the conference?
Columns: ['School', 'City', 'Mascot', 'County', 'Year joined', 'Previous Conference', 'Year Left', 'Conference Joined']
Types: ['text', 'text', 'text', 'text', 'real', 'text', 'real', 'text']
Sample row: ['East Chicago Roosevelt', 'East Chicago', 'Roughriders', '45 Lake', 1963.0, 'Northern Indiana', 1968.0, 'Indiana Lake Shore']
SQL:

assistant: SELECT "Year Left" FROM "Table" WHERE "Mascot" = 'Roughriders';