返回行数组

我有一个数据库，我正在查询:"select email from users where access=1"。我收到的错误是

致命错误:在非对象上调用成员函数query(): $result = $mysqli->query($query);

我使用http://uk3.php.net/manual/en/mysqli.query.php作为参考，我看不到我在哪里查询过程和面向对象的PHP的混合物。

<?php
$db_host = "";
$db_user = "";
$db_pass = "";
$db_name = "";
/* OOP MYSQLI DATABASE CONNECTION */
$db = new mysqli($db_host, $db_user, $db_pass, $db_name);
if ($mysqli->connect_error) {
    die('Connect Error (' . $mysqli->connect_errno . ') '
            . $mysqli->connect_error);
}
/*LOGIN QUERY */
$query = "select email from users where access=1";
$result = $mysqli->query($query);
$email= $result->fetch_array(MYSQLI_NUM);    
if(isset($email[0])){    
    $query1="select id from user where email='".$email[0]."' and facebook=1";
    $result1 = $mysqli->query($query1);
    $email1= $result1->fetch_array(MYSQLI_NUM);  
    $userId=$admin[0];
}
?>