Name the barrel length for rear sight a2 for factory compensator
CREATE TABLE table_12834315_4 (
    barrel_length VARCHAR,
    rear_sight VARCHAR,
    muzzle_device VARCHAR
)
SELECT barrel_length FROM table_12834315_4 WHERE rear_sight = "A2" AND muzzle_device = "Factory compensator"
Below are sql tables schemas paired with instruction that describes a task. Using valid SQLite, write a response that appropriately completes the request for the provided tables. ### Instruction: Name the barrel length for rear sight a2 for factory compensator ### Input: CREATE TABLE table_12834315_4 (
    barrel_length VARCHAR,
    rear_sight VARCHAR,
    muzzle_device VARCHAR
) ### Response: SELECT barrel_length FROM table_12834315_4 WHERE rear_sight = "A2" AND muzzle_device = "Factory compensator"