Magento – Best way to manage Resellers

Try to add this function to your collection class. My logic is you have sum of points grouping by below of 0 and above of 0 and all of them.

class My_Module_Model_Mysql4_Registry_Collection extends Mage_Core_Model_Mysql4_Collection_Abstract
{
    public function _construct()
    {
        $this->_init('mymodule/registry');
    }

    public function getSumOfPoints($customerId)
    {
        $this->addFieldToFilter('customer_id', $customerId);

        $this->getSelect()
            ->reset('columns')
            ->columns(new Zend_Db_Expr("sign(points) as sign"))
            ->columns(new Zend_Db_Expr("sum(points) as summ"))
            ->group(new Zend_Db_Expr("sign(points)"));
        return $this;
    }
}

And you can get results by calling this function at anywhere:

$results = Mage::getResourceModel('mymodule/registry_collection')->getSumOfPoints($customerId);
foreach ($results as $result) {
    print_r($result->getData());
}

If you put all above correctly it will give result like these:

Array
(
    [sign] => -1 //summ of points less than 0
    [summ] => -166
)
Array
(
    [sign] => 1 //summ of points great than 0
    [summ] => 312
)

You can get summ of all points adding two result above. If you don't want to use collection class you can adopt this logic to your own code which is using resource model. Collection class generates sql query given below, try first this query, if it gives appropriate result you can use code given above:

SELECT
    sign(points)AS sign,
    sum(points)AS summ
FROM
    `mymodule_registry` AS `main_table` //put here real table name
WHERE
    (customer_id = '4') //put real customer id
GROUP BY
    sign(points)

I would suggest that you start with the basics, which you already can find in small books like "Magento PHP Developer's Guide" or similar.

And then, besides of a running Magento installation and a powerful IDE (I prefer PhpStorm), you need a lot of time for hands on.

Try to dig deep into the core of Magento, the official and free study guide is a good way to start.

And last but not least, code, code, code, code......

It took me at least more than a year working with Magento until I was able to pass the Magento Certified Developer exam.