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
Hope this helps. Thanks.
来自：http://blog.chapagain.com.np/magento-collection-functions/