Magento: Very Useful Collection Functions

There are different important functions that you can implement in your Collection object. The functions are present in Varien_Data_Collection_Db class. The class file is present in lib/Varien/Data/Collection/Db.php
Here are some of the functions that you can use in your collection object:-

/**  * Get Zend_Db_Select instance  */ $collection->getSelect();   /**  * Get collection size  */ $collection->getSelect()->getSize();   /**  * Get sql select string or object  */ $collection->getSelect()->getSelectSql();   /**  * Add select order  */ $collection->getSelect()->setOrder($field, $direction);   /**  * Add field filter to collection  *  * If $attribute is an array will add OR condition with following format:  * array(  *     array('attribute'=>'firstname', 'like'=>'test%'),  *     array('attribute'=>'lastname', 'like'=>'test%'),  * )  */ $collection->getSelect()->setOrder($field, $condition);   /**  * Set select distinct  */ $collection->getSelect()->distinct($flag);   /**  * Get all data array for collection  */ $collection->getSelect()->getData();   /**  * Reset loaded for collection data array  */ $collection->getSelect()->resetData();   /**  * Print and/or log query  */ $collection->getSelect()->printLogQuery(true, true);

More functions below:-
Varien_Data_Collection_Db class extends Varien_Data_Collection class. Here are some more functions present in Varien_Data_Collection class:-

/**  * Get current collection page  */ $collection->getSelect()->getCurPage();   /**  * Retrieve collection last page number  */ $collection->getSelect()->getLastPageNumber();   /**  * Retrieve collection page size  */ $collection->getSelect()->getPageSize();   /**  * Retrieve collection all items count  */ $collection->getSelect()->getSize();   /**  * Retrieve collection first item  */ $collection->getSelect()->getFirstItem();   /**  * Retrieve collection last item  */ $collection->getSelect()->getLastItem();   /**  * Retrieve collection items  */ $collection->getSelect()->getItems();   /**  * Clear collection  */ $collection->getSelect()->clear();

You can also use the select functions as present in Zend_Db_Select class. This class file is present in lib/Zend/Db/Select.php