DB<120> @order=1..5
 => (1, 2, 3, 4, 5)

  DB<121> $last= $order[0]
 => 1

  DB<122> for $cur (@order[1..$#order]) {
           print "$last,$cur\t";
           $last =$cur;
           }
 => ""
1,2	2,3	3,4	4,5	

##</code><code>##

  DB<126> use List::Util qw/reduce/

  DB<127> reduce { print "$a,$b\n"; $b } @order
1,2
2,3
3,4
4,5

##</code><code>##

while ( my $rec = $data->fetchrow_hashref ) {
    push @{ $result{ $rec->{"ID"} } }, $rec->{"item"};
    push @order, $rec->{ID};
}