How do I combine two product collections into one observer?

Question

Can this be added to an observer like in my code in: How to set products in stock after import ?

I currently have a module I created that will check the sites prices.
It is currently just a page inside the admin that will show all the products that have special prices in a table.
The code itself is simple.
Check if the special price is equal to the product price or if it is equal to 0.
If it is change it to a blank.

<?php
    $_productCollection = Mage::getModel('catalog/product')->getCollection(); /* get the collection */
    $_productCollection->addAttributeToSelect('*'); /* select all attributes */
    $_productCollection->addAttributeToFilter('special_price', ['notnull' => true]); /* check if special_price is not null or empty */
    $_productCollection->addAttributeToSort('special_price', 'asc'); /* sort the special price */
    $_productCollection->getSelect(); /* get selection from database */
    Mage::getModel('review/review')->appendSummary($_productCollection); /* i have no idea what this does */
    $_helper = $this->helper('catalog/output');
    foreach ($_productCollection as $_product):
        $price = $_product->getPrice(); /* value of price */
        $specialprice = $_product->getSpecialPrice(); /* value of special price */
        $tprice = trim($price);
        $tspecialprice = trim($specialprice);
        /* check if special price equal to price and set empty */
        if($tprice==$tspecialprice) {
            $_product->setSpecialPrice("");
            $_product->getResource()->saveAttribute($_product, 'special_price');
        }
        /* check if special price equal to zero and set empty */
        if($tspecialprice==0) {
            $_product->setSpecialPrice("");
            $_product->getResource()->saveAttribute($_product, 'special_price');
        }
    endforeach;
?>

Can this be optimized?

Answer 1

I'm not sure what you are trying to achieve, but you can get the products that have a discount using a single query like this:

$discounted = Mage::getModel('catalog/product')->getCollection();
$discounted->addExpressionAttributeToSelect('discount_value', '(({{price}} - final_price))', array('price'));
$this->getSelect()->having('discount_value > ?' , 0);

This should get you started.

This is even better than working with only special price since the discounts can come from discount rules also.