my $sth_box_name = $dbh->prepare("SELECT box_name FROM navibox") or die $dbh->errstr;
my $sth_links = $dbh->prepare("SELECT id,link_titel,link,categorie,box_name,option,content FROM navigation WHERE box_name=?") or die $dbh->errstr;

$sth_box_name->execute or die $dbh->errstr;

my @boxes;

while( my $box_name = $sth_box_name->fetchrow_array ) {

    $sth_links->execute($box_name);

    my @links;
    while( my $hashref = $sth_links->fetchrow_hashref ) {
        push @links, { link => $hashref->{link} };
    }

    push @boxes, { box_name => $box_name, box_links => \@links };

}

$sth_box_name->finish();  
$sth_links->finish();