What is the id of the files that are available in the format of mp4 and a resolution smaller than 1000?
SELECT f_id FROM files WHERE formats  =  "mp4" INTERSECT SELECT f_id FROM song WHERE resolution  <  1000
SELECT f_id FROM files WHERE formats  =  "mp4" INTERSECT SELECT f_id FROM song WHERE resolution  <  1000
[{'f_id': 3}, {'f_id': 6}]