Sum of all customer's orders returns 0 on status: complete

Question

1. My function returns 0 on total sum of orders from a client when status is set to complete. When status is set to processing, everything goes O.K. Is it the right way to obtain a complete status?
2. Also, I want to get all the SKUs from the customer of all orders. I tried to change getGrandTotal to getSku() but it returns nothing.

The code:

$customer_email = Mage::getSingleton('customer/session')->getCustomer()->getEmail();
$collection = Mage::getModel('sales/order')->getCollection()
    ->addFieldToFilter('status', 'complete')
    ->addAttributeToFilter('customer_email', array('like' => $customer_email));

foreach ($collection as $order) {
    //do something
    //echo round($order->getGrandTotal(), 2) . " ";
    $sum += $order->getGrandTotal();
}

echo round($sum,2); ?>

Answer 1

There is one case when the result can be 0.
Your collection does not have items.
Check what $collection->count() returns.
Well there is actually an other case, but I assume you did not modify the getGrandTotal() method.

Answer 2

Nr (2): To get all SKU's you could do...

$skus = array();
foreach ($collection as $order) {
    foreach ($order->getAllItems() as $item) {
        $skus[] = $item->getSku();
    }
}