CREATE TABLE files (duration INTEGER, f_id VARCHAR, formats VARCHAR); CREATE TABLE song (f_id VARCHAR, resolution VARCHAR)
What is the average duration of songs that have mp3 format and resolution below 800?
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