ORDER BY 2 is positional and brittle; ordering by a column absent from SELECT DISTINCT is undefined.

Ordinals bind to the SELECT list's shape, not to meaning — write-once convenience that becomes a landmine the first time anyone edits the columns (the insert_select_position family, ORDER-BY-flavored). The DISTINCT case is the same logical-order lesson HAVING and QUALIFY taught: ORDER BY runs on the output, and DISTINCT's output no longer carries unselected columns.

SELECT
  bpm,
  song
FROM
  setlist
ORDER BY
  2 DESC;

SELECT
  bpm,
  song
FROM
  setlist
ORDER BY
  bpm DESC;

After a column was reordered, ORDER BY 2 sorted by the song name, not the bpm — an ordinal binds to the SELECT list's position, so editing the columns silently changes what you sort by; naming the column is stable.

Named columns/aliases in ORDER BY; ordinals only in throwaway console work.