$sql ="SELECT fields.. FROM customer
INNER JOIN addresses USING(customer_id )
WHERE customer_id = 123
";

$statement = $this->connection->query($sql);

$loadedCustomers = [];
while($row = $statment->fetch()){
if(!isset($loadedCustomers[$row->customer_id])){
$customer = $customerHydrator->createFromStdObject($row);
$loadedCustomers[$row->customer_id] = $customer;
}
$customer = $loadedCustomers[$row->customer_id];
$address = $addressHydrator->createFromStdObject($row);
$customer->addAddress($address);
}

return array_values($loadedCustomers);