Zend_Db_Mysqli strange

<?php
// Ensure library/ is on include_path
set_include_path(implode(PATH_SEPARATOR, array(
    realpath('./library'),
    get_include_path(),
)));

/** Zend_Application */
require_once 'Zend/Loader.php';
Zend_Loader::loadClass('Zend_Config_Ini');
Zend_Loader::loadClass('Zend_Db');

$params = array(
    'adapter' => 'mysqli',
    'params' => array(
        'host'      => 'localhost',
        'dbname'    => 'test',
        'username'  => 'root',
        'password'  => ''
    )
);

$db = \Zend_Db::factory($params['adapter'], $params['params']);

$curtimeStmt = $db->query("SELECT CURTIME()");

$nowStmt = $db->query("SELECT NOW()");

$s = $curtimeStmt->fetch();
var_dump($s);// false. Where is curtime?!