либо немного изменить

SELECT EXTRACT(YEAR FROM CAST(i.invoice_date AS DATE)) AS year_of_invoice,
       COUNT(DISTINCT t.name) AS unique_track_count
FROM invoice AS i
LEFT JOIN invoice_line AS il ON i.invoice_id = il.invoice_id
LEFT JOIN track AS t ON il.track_id = t.track_id
GROUP BY year_of_invoice;