user: Question: Name the barrel length for rear sight A2 for Factory compensator
Columns: ['Colt model no.', 'Name', 'Stock', 'Fire control', 'Rear sight', 'Forward assist', 'Case deflector', 'Barrel length', 'Barrel profile', 'Barrel twist', 'Hand guards', 'Bayonet Lug', 'Muzzle device']
Types: ['text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['CR6724', 'Colt Accurized Rifle', 'A2', 'S-1', 'Flattop', 'Yes', 'Yes', '24 in.', 'Stainless HBAR', '1:9', 'FF Tube', 'No', 'None']
SQL:

assistant: SELECT "Barrel length" FROM "Table" WHERE "Rear sight" = 'A2' AND "Muzzle device" = 'Factory compensator';