Useful Collection Functions of Magento
$collection->getSelect();
To get select string of sql object
$collection->getSelect()->getSelectSql();
To get the size of collection
$collection->getSelect()->getSize();
To get distinct selection
$collection->getSelect()->distinct($flag);
To get all data array for collection
$collection->getSelect()->getData();
To set an order to the collection
$collection->getSelect()->setOrder($field, $direction);
To print the query or log the query
$collection->getSelect()->printLogQuery(true, true);
To get collection items
$collection->getSelect()->getItems();
To get first item of the collection
$collection->getSelect()->getFirstItem();
To get last item of the collection
$collection->getSelect()->getLastItem();
To get current collection page number
$collection->getSelect()->getCurPage();
To get total collection pages
$collection->getSelect()->getPageSize();
To clear the collection
$collection->getSelect()->clear();