use DBIx::Simple;

my $db = DBIx::Simple->connect("...",{RaiseError => 1} ) or die "can't\n";

for my $cust ($db->query('SELECT cust_ID, cust_name FROM customer')->hashes) {
    for my $order ($db->query('SELECT * FROM orders WHERE cust_ID = ?', $cust->{cust_ID}->hashes) {
        # code
    }
}