bad_authors_or_songs.sql

select * from readers_items r
join items i on i.item_id = r.item_id
left join songs s on s.song_id = i.song_id
left join authors a on a.author_id = s.author_id
where r.reader_id = %reader_id here%
and (a.author_id is null or s.song_id is null)