How to print exact sql query in zend framework ?

I have the following piece of code which i taken from model,

    ...
                  $select = $this->_db->select()
                    ->from($this->_name)
                    ->where('shipping=?',$type)
                    ->where('customer_id=?',$userid);
                 echo  $select; exit; // which gives exact mysql query.
            .....

When i use update query in zend like ,

$up_value = array('billing'=> '0');
$this->update($up_value,'customer_id ='.$userid.' and address_id <> '.$data['address_Id']);      

Here i want to know the exact mysql query. Is there any possible way to print the mysql query in zend ? kindly advice

Select objects have a __toString() method in Zend Framework.

From the Zend Framework manual:

$select = $db->select()
             ->from('products');

$sql = $select->__toString();
echo "$sql\n";

// The output is the string:
//   SELECT * FROM "products"

An alternative solution would be to use the Zend_Db_Profiler. i.e.

$db->getProfiler()->setEnabled(true);

// your code
$this->update($up_value,'customer_id ='.$userid.' and address_id <> '.$data['address_Id']); 

Zend_Debug::dump($db->getProfiler()->getLastQueryProfile()->getQuery());
Zend_Debug::dump($db->getProfiler()->getLastQueryProfile()->getQueryParams());
$db->getProfiler()->setEnabled(false);

http://framework.zend.com/manual/en/zend.db.select.html