PHP登录系统Mysql

Question

我正在尝试从我正在关注的教程中创建一个php登录系统，用于我正在创建的Android应用程序的登录，但是我收到此错误：

  

警告：mysqli_num_rows（）要求参数1为mysqli_result，第7行的C：\ wamp \ www \ login.php中给出布尔值

我知道我的代码不安全但有人可以帮助我吗？

login.php

<?php
require"db.php";
$user_name = "user";
$user_pass = "pass";
$mysql_qry = "select * from users where username like '$user_name' and password '$user_pass';";
$result = mysqli_query($conn, $mysql_qry);
if (mysqli_num_rows($result) > 0) { // line 7 code where the error is
    echo "login success";
}
else {
    echo "not success";
}
?>

db.php中：

<?php

$db_name = "hash";
$mysql_username = "root";
$mysql_password = "";
$dbname = "hash";
$server_name = "localhost";
$conn = mysqli_connect($server_name, $mysql_username, $mysql_password,     $db_name);

if ($conn) {
    echo "Success";
}
else{
    echo "not success";
}

?>