user: Question: What is the national cup statistics when the Championship is 21 app / 6 goals?
Columns: ['Season', 'Club', 'Country', 'Championship', 'National Cup', 'International Cup']
Types: ['text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['2006–2007', 'CA Bizerte', 'Tunisian Ligue', '? app / 0 goals', '– app / – goal', '– app / – goal']
SQL:

assistant: SELECT "National Cup" FROM "Table" WHERE "Championship" = '21 app / 6 goals';