PHP PDO删除rowCount始终返回0

PHP 5.2.17 (cli) (built: Jan 17 2011 12:51:24) Copyright (c) 1997-2010 The PHP Group Zend Engine v2.2.0, Copyright (c) 1998-2010 Zend Technologies

Here is my function

public function remove($id){
        $params = array(':id' => $id);
        $delete_loan = $this->ext_conn->prepare("DELETE FROM loan_program WHERE id = :id");
        $delete_loan->exec($params);
        $affected_rows = $delete_loan->rowCount();  //and not this?
        if ($affected_rows == 1) {
            return array('status' => 'success');
        } else {
            return array('status' => 'failure', 'reason' => 'delete_failed', 'rowcount' => $affected_rows, 'errornfo' => $delete_loan->errorInfo());
        }
    }

I'm calling it and passing an id of the row in the database. The row gets removed from the database, but the if ($affected_rows == 1) { is always false. errorInfo() returns an array of [0] => 0000.

I've been through the PDO manual and I was referencing http://wiki.hashphp.org/PDO_Tutorial_for_MySQL_Developers#INSERT.2C_DELETE.2C_UPDATE_Prepared_Queries

Shouldn't rowcount() return 1 (or however many id's had the value passed to remove?

Thanks in advance.

PDO::exec expects an SQL statement string. If you prepare a statement, you must call PDOStatement::execute instead

$delete_loan->execute($params);