SELECT AVG(T1.duration) FROM files AS T1 JOIN song AS T2 ON T1.f_id = T2.f_id WHERE T1.formats = "mp3" AND T2.resolution < 800
Berapa durasi rata -rata lagu yang memiliki format dan resolusi MP3 di bawah 800?
CREATE TABLE files (duration INTEGER, f_id VARCHAR, formats VARCHAR); CREATE TABLE song (f_id VARCHAR, resolution VARCHAR)