What are the ids of all songs that are available on mp4 or have a higher resolution than 720?
SELECT f_id FROM files WHERE formats  =  "mp4" UNION SELECT f_id FROM song WHERE resolution  >  720
SELECT f_id FROM files WHERE formats  =  "mp4" UNION SELECT f_id FROM song WHERE resolution  >  720
[{'f_id': 1}, {'f_id': 3}, {'f_id': 4}, {'f_id': 6}]