Feeds Query

Is there an example or guide to see feeds query? what kind of syntax it uses and stuff like that just using regular SQL query produces error.
SELECT jos_melsongs.id, jos_melsongs.name, jos_melsongs.audio_folder, jos_melsongs.dur_hrs,jos_melsongs.dur_mins, jos_melsongs.dur_secs, jos_melfilepath.folder FROM jos_melsongs JOIN jos_melfilepath ON jos_melsongs.audio_folder=jos_melfilepath.id ORDER BY jos_melsongs.id DESC LIMIT 50

{"result":"error", "error":"Table '{table omited}.#__melsongs join' doesn't exist"}