Какая ошибка в коде:SELECT t.name,
i.unit_price,
pt.playlist_id,
p.name– укажи необходимое поле
FROM track AS t
INNER JOIN invoice_line AS i ON t.track_id=i.track_id
INNER JOIN playlist_track AS pt ON t.track_id=pt.track_id
INNER JOIN playlist AS p ON pt.track_id=p.playlist_id
WHERE t.name IS NOT NULL AND i.unit_price IS NOT NULL AND p.name IS NOT NULL
GROUP BY t.name, i.unit_price, pt.playlist_id, p.name
LIMIT 20;