user: Question: What is the least value for average attendance when average on previous season is +644?
Columns: ['Season', 'Ave. Attendance', '+/- ave. on prev. season', 'Competition', 'Occupier']
Types: ['text', 'real', 'text', 'text', 'text']
Sample row: ['1992–93', 322.0, 'N/A', 'Southern Football League', 'Rushden and Diamonds']
SQL:

assistant: SELECT MIN("Ave. Attendance") FROM "Table" WHERE "+/- ave. on prev. season" = '+644';