登录功能根本不起作用

Question

我有这段代码：

<?php
include("config.php");
session_start();

if($_SERVER["REQUEST_METHOD"] == "POST") {
    // username and password sent from form 

    $myusername = mysqli_real_escape_string($db,$_POST['username']);
    $mypassword = mysqli_real_escape_string($db,$_POST['password']); 

    $sql = "SELECT id FROM admin WHERE username = '$myusername' and passcode = '$mypassword'";
    $result = mysqli_query($db,$sql);
    $row = mysqli_fetch_array($result,MYSQLI_ASSOC);
    $active = $row['active'];

    $count = mysqli_num_rows($result);

    // If result matched $myusername and $mypassword, table row must be 1 row

    if($count == 1) {
        session_register("myusername");
        $_SESSION['login_user'] = $myusername;

        header("location: welcome.php");
    }else {
        $error = "Your Login Name or Password is invalid";
    }
}?>

当我尝试登录（使用现有的数据库凭据）时，它会返回：

  

警告：mysqli_fetch_array（）要求参数1为mysqli_result，第13行的/home/avelar.xyz/public/dev/login-em-php/login.php中给出布尔值警告：mysqli_num_rows（）要求参数1为是mysqli_result，第16行/home/avelar.xyz/public/dev/login-em-php/login.php中给出的布尔值

错误在哪里？