Re: Confusing order by error

I'm hoping someone can give us a little help understanding an error in the ORDER BY clause, because when I read https://www.postgresql.org/docs/9.5/static/sql-select.html#SQL-ORDERBY I just don't see anything that explains the behavior.

    SELECT t1.pk, t1.name, t1.ref, CONCAT( t2.id , ':', t2.name )  AS ref_display
      FROM test_table as t1
 LEFT JOIN test_table as t2 ON  t1.ref = t2.pk
  ORDER BY name;

  
    SELECT t1.pk, t1.name, t1.ref, CONCAT( t2.id , ':', t2.name )  AS ref_display
      FROM test_table as t1
 LEFT JOIN test_table as t2 ON  t1.ref = t2.pk
  ORDER BY UPPER(name);

ERROR:  column reference "name" is ambiguous
LINE 4:   ORDER BY UPPER(name);
                         ^

Eh? The parser (or whatever phase) understood "ORDER BY name" in the first query, so why did that UPPER() string function make a difference in the second query?