What's problem of the database query code in this post?

This is part of the code

$loc=JRoute::_($loc);
            $arr=array();
			$arr=split("&",$loc);
			$myurl=$arr[0]."&".$arr[3]."&".$arr[2]."&".$arr[4]."&".$arr[1];
			//here we begin sef url,we need to get url structure like this index.php?option=com_content&catid=10&id=109&lang=en&view=article first
			$epdb     =& JFactory::getDBO();
		$epquery="SELECT oldurl FROM rev_redirection WHERE newurl ='".$myurl."'";
//$epquery="SELECT oldurl FROM rev_redirection WHERE newurl ='index.php?option=com_content&catid=9&id=111&lang=en&view=article' LIMIT 10";
		$epdb->setQuery($epquery);
		$epresult=$epdb->loadResult();
		$eperror=$epdb->getErrorMsg($epresult);
		$newloc="Result:".$epresult."Error:".$eperror."Url:".$myurl."Query:".$epquery;

PHP:

here is one of the results

Result:Error:Url:index.php?option=com_content&catid=14&id=171&lang=en&view=articleQuery:SELECT oldurl FROM rev_redirection WHERE newurl ='index.php?option=com_content&catid=14&id=171&lang=en&view=article'

PHP:

and when I query this

SELECT oldurl FROM rev_redirection WHERE newurl ='index.php?option=com_content&catid=14&id=171&lang=en&view=article'

PHP:

in mysql,it runs successful,returns the result I want,but here in this code,when I can't get the result?thanks in advance