The "Statement Handle Attributes" section of the DBI docs (perldoc DBI) documents the NAME, NAME_lc, NAME_uc attributes as being read-only array-refs (whereas $sth->fetchrow_array is documented as returned an array of the values). So you need to assign these values to a scalar and treat it as an array ref:

  my $fieldNames = $sth->{NAME_UC};
  print join ":", @$fieldNames;
[download]