Searching for SKU without special characters

To make this work for both, the real SKU and the one without -, both have to be added to catalogsearch_result table because SQL-query for search results looks like this:

SELECT `s`.`product_id`, 0 AS `relevance`
FROM `catalogsearch_fulltext` AS `s`
INNER JOIN `catalog_product_entity` AS `e` ON e.entity_id = s.product_id
WHERE (s.store_id = 1) AND ((`s`.`data_index` LIKE '%sku-123%'))

I will not give an answer where you have to override core files and I'm still playing arround with catalog search reindexing process to find a way to make it work event-observer based.

As (temporarily?) solution that ends up in the same result as modifiying index process, you can do this:

1. create a new searchable product attribute from backend, let's call it sku_search
2. add an observer that listens to catalog_product_save_before to "autofill" this attribute
3. Reindex Catalog Search Index
4. DONE.

Observer code could look like this:

class My_Module_Model_Observer extends Mage_Core_Model_Observer
{
    public function setSkuSearchAttribute($observer)
    {
        $product = $observer->getProduct();
        $product->setSkuSearch(str_replace('-', '', $product->geSku()));
    }
}

I would add something, to prevent that this attribute is manually edited from backend, like another observer for catalog_product_edit_action with this code:

class My_Module_Model_Observer extends Mage_Core_Model_Observer
{
    public function lockProductAttribute(Varien_Event_Observer $observer)
    {
        $product = $observer->getProduct();
        $product->lockAttribute('sku_search');
    }
}