user: Question: Name the total number of material collected for  Justice League of America by George Pérez, Vol. 2
Columns: ['#', 'Volume line', 'Volume title', 'Creators', 'Material collected', 'Publication date', 'ISBN']
Types: ['real', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: [1.0, 'Superman', 'Kryptonite Nevermore', "Dennis O'Neil Curt Swan", 'Superman #233-238, #240-242', '2009/01/28', '978-1401220853']
SQL:

assistant: SELECT "Material collected" FROM "Table" WHERE "Volume title" = 'Justice League of America by George Pérez, Vol. 2';