Magento Filter By Relative Value - magento

Question

I would like to filter a collection by relative value per that row. For example,
SELECT * FROM table WHERE column_1 > column_2
The only thing I know how to do in Magento would be
$q = Mage::getModel('table')->getCollection()
->addAttributeToFilter('column_1', array('gt' => $some_number));
or something of that sort. I can only give it a value to compare against, not a column name. I also looked at the Zend_Db_Select method at the where clause but didn't find anything that would help. Do I actually have to go all the way down to a direct SQL query (something which is, of course, avoided at all costs)? (I'm running Magento 1.3.2.4)
Thank you.

Answer 1

Try something like
$q = Mage::getModel('table')->getCollection()
->addAttributeToSelect('column_1')
->addAttributeToSelect('column_2')
->addAttributeToFilter('column_1', array('gt' => Zend_Db_Expr('`column_2`')));

Answer 2

OK, this is probably not the ideal solution, but it's one way of getting what you need.
This is how I got a collection of products that were on sale, where a products final price is lower than its price.
I first made a new empty data collection. Then defined the collection I was going to loop through filtering what I could first. After that I looped through that collection and any products that matched my requirements got added to the empty collection.
$this->_itemCollection = new Varien_Data_Collection();
$collection = Mage::getResourceModel('catalog/product_collection');
$collection->setVisibility(Mage::getSingleton('catalog/product_visibility')->getVisibleInCatalogIds());
$category = Mage::getModel('catalog/category')->load($this->getCategoryId());
$collection = $this->_addProductAttributesAndPrices($collection)
->addStoreFilter()
->addCategoryFilter($category)
->addAttributeToSort('position', 'asc');
$i=0;
foreach($collection as $product){
if($product->getFinalPrice() > $product->getPrice() && !$this->_itemCollection->getItemById($product->getId())){
$this->_itemCollection->addItem($product);
$i++;
}
if($i==$this->getProductsCount()){
break;
}
}
$this->setProductCollection($this->_itemCollection);