Magento自动生成产品SKU,有两种方法
方法一：

Open/app/design/adminhtml/default/default/template/catalog/product/edit.phtmland add the following code to the bottom of the file:

<?php
    $dbread = Mage::getSingleton('core/resource')->getConnection('core_read');
    $sql = $dbread->query("SELECT * FROM catalog_product_entity ORDER BY created_at DESC LIMIT 1");
    $res = $sql->fetch();
?>
<script type="text/javascript">
if(document.getElementById('sku').value == ""){
    document.getElementById('sku').value = <?php echo (int)$res["sku"] + 1; ?>;
}
</script>

Note:Read the SKU (must be an integer) of the last added product.
Increment the SKU by 1.
Pre-populate the incremented new SKU to the SKU field by JavaScript.

方法二：

打开 app/code/core/Mage/Adminhtml/controllers/Catalog/ProductController.php

line 743:

/**
 * Save product action
 */
public function saveAction()
{
    $storeId        = $this->getRequest()->getParam('store');
    $redirectBack   = $this->getRequest()->getParam('back', false);
    $productId      = $this->getRequest()->getParam('id');  
    $isEdit         = (int)($this->getRequest()->getParam('id') != null);

    $data = $this->getRequest()->getPost();
	
	//===> 这里开始
	if(isset($data['category_ids']) AND $data['category_ids']) $category_ids = array_filter(array_unique(explode(',', $data['category_ids'])));
	if(!$category_ids) if($productId) $category_ids = array_filter(Mage::getModel('catalog/product')->load($productId)->getCategoryIds());
	
	$_categories = array();
	foreach ($category_ids as $category_id) 
	{
		if($category_id)
		{
			$_cat = Mage::getModel('catalog/category')->load($category_id);
			$_cat->getLevel()*1 == 2 ? $_categories[$_cat->getId()]['name'] = $_cat->getName() : $_categories[$_cat->getParentId()]['son'][$_cat->getId()] = $_cat->getName();
		}
	}
	
	$_first_category = current($_categories);
	if(!$_first_category) exit('<script>alert("Please Choose any Product Category !");history.back();</script>');
	
	if(!$productId OR ($productId AND !$data['product']['sku']))
	{
		$prefix = '';
		if(stripos('+'.$_first_category['name'], 'decals')) $prefix .= 'D-';
		if(isset($_first_category['son'])) $prefix .= strtoupper(substr($_first_category['name'], 0, 1).substr(current($_first_category['son']), 0, 1));
		else $prefix .= strtoupper(substr($_first_category['name'], 0, 2));
		
		$dbread                 =   Mage::getSingleton('core/resource')->getConnection('core_read');
		$sql                    =   $dbread->query("SELECT * FROM mgy2_catalog_product_entity WHERE `sku` LIKE '".$prefix."%' ORDER BY `entity_id` DESC LIMIT 1 ");
		$row                    =   $sql->fetch();
		$next_sku_num           =   abs(substr($row['sku'], -4)*1)+1;
		$next_sku_len           =   strlen($next_sku_num)*1;
		$next_sku               =   $prefix.($next_sku_len < 4 ? str_repeat('0',(4-$next_sku_len)) : '').$next_sku_num;
		$_POST['product']['sku'] =& $next_sku;
	}
	//===> 这里结束	
	
    if ($data) 
    {
        $this->_filterStockData($data['product']['stock_data']);

        $product = $this->_initProductSave();
		
		// echo '<pre>'; print_r($data); echo '</pre>'; die;	

        try {
            $product->save();
            $productId = $product->getId();

            if (isset($data['copy_to_stores'])) {
               $this->_copyAttributesBetweenStores($data['copy_to_stores'], $product);
            }

            $this->_getSession()->addSuccess($this->__('The product has been saved.'));
        } catch (Mage_Core_Exception $e) {
            $this->_getSession()->addError($e->getMessage())
                ->setProductData($data);
            $redirectBack = true;
        } catch (Exception $e) {
            Mage::logException($e);
            $this->_getSession()->addError($e->getMessage());
            $redirectBack = true;
        }
    }

    if ($redirectBack) {
        $this->_redirect('*/*/edit', array(
            'id'    => $productId,
            '_current'=>true
        ));
    } elseif($this->getRequest()->getParam('popup')) {
        $this->_redirect('*/*/created', array(
            '_current'   => true,
            'id'         => $productId,
            'edit'       => $isEdit
        ));
    } else {
        $this->_redirect('*/*/', array('store'=>$storeId));
    }
}

原理如下：

Wall decals
D-WA0001

Car decal
Bumper – D-CB0001
Car – D-CC0001
Mirror D-CM0001

MACBOOK DECALS
Macbook or Laptop – D-MM0001
Trackpad – D-MT0001

iPad
IPad – D-IP0001
IPad mini – D-IM0001

原理自己计算吧