push @$sort_by_str, @{ $sort_spec->{tiebreaker} };
$sort_by_str = join(', ', map { "${_} ${sort_dir_str}${nulls_str}" } @{ $sort_by_str });
push @$sort_by_str, @{ $sort_spec->{tiebreaker} };
$sort_by_str = join(', ', map { "${_} ${sort_dir_str}${nulls_str}" } @{ $sort_by_str });