text: insert into PLAYLISTTRACK (PLAYLISTID, TRACKID) 
  (
      SELECT 2, TRACKID FROM
  (
      SELECT TRACK.TRACKID FROM TRACK
      INNER JOIN INVOICELINE
      ON TRACK.TRACKID = INVOICELINE.TRACKID
      GROUP BY TRACK.TRACKID
      ORDER BY COUNT(INVOICELINE.INVOICELINEID) DESC
  )
  WHERE ROWNUM <= 2
  );