CREATE TABLE files (f_id VARCHAR2, formats VARCHAR2, resolution NUMBER)
CREATE TABLE song (f_id VARCHAR2, formats VARCHAR2, resolution NUMBER)

Find the id of songs that are available in mp4 format and have resolution lower 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