push @$result, $row while ($row = $sth->fetchrow_hashref());

...
use Storable;
my $hashref = $dbh->selectall_hashref($statement);

Storable::store($hashref,'datei.ser') or die "Konnte datei.ser nicht schreiben: $!";
undef $hashref;
$hashref = Storable::retrieve('datei.ser') or "Konnte datei.ser nicht lesen: $!";

use Data::Dumper;
print Data::Dumper::Dump($hashref);
# ungetestet

while (my @array = $sth->fetchrow()) {

while (my $arrayRef = $sth->fetchrow_arrayref()) {
  my @array = @$arrayRef; # oder besser direkt mit $arrayRef arbeiten

while (my $hashRef = $sth->fetchrow_hashref()) {
  my %hash = %$hashRef; # oder besser direkt mit $hashRef arbeiten

while ($sth->{syb_more_results}) {
  while (my @array = $sth->fetchrow) {

while (my @array = $sth->fetchrow()) {

mysql> use test;
Database changed
mysql> show tables;
Empty set (0.00 sec)

mysql> create table nulltest (leeresfeld int(1) default null);
Query OK, 0 rows affected (0.02 sec)

mysql> insert into nulltest values (null);
Query OK, 1 row affected (0.01 sec)

mysql> select * from nulltest;
+------------+
| leeresfeld |
+------------+
|       NULL |
+------------+
1 row in set (0.02 sec)

mysql>\q
Bye
format_c@server:~> cd perl_scripts/
format_c@server:~/perl_scripts> vi test.pl
format_c@server:~/perl_scripts> cat test.pl && perl test.pl
use strict;
use DBI;
my $dbh = DBI->connect('DBI:mysql:database=test;host=localhost;','test','test')
        or die DBI::errstr();
my $sth = $dbh->prepare('SELECT * FROM nulltest') or die $dbh->errstr();
$sth->execute() or die $dbh->errstr();

my $i = 0;
while (my @row = $sth->fetchrow_array()) {
        print ++$i,"\n";
}
$sth->finish();
$dbh->disconnect();

exit;

1
format_c@server:~/perl_scripts>

while (my ($x, $y) = $sth->fetchrow()) {
  ...