Myqli php login

我刚刚开始使用mysqli，我正在尝试连接到数据库并登录，我收到错误消息，

注意：未定义的索引：___mysqli_ston在E：''EasyPHP-DevServer-14.1VC11''data''localweb''my portable files''course work''login.php第14行

我还尝试在表单页面上显示错误消息，而不是创建当前正在执行的新页面。 我忘记了 PHP 是否必须在同一页面上才能显示错误？

警告：mysqli_query（） 期望参数 1 为 mysqli，空值在第 14 行的 E：''EasyPHP-DevServer-14.1VC11''data''localweb''my portable files''course work''login.php

找不到数据库

<?php
session_start();
$username = $_POST['username'];
$password = $_POST['password'];
$errors = array();

if ($username&&$password)
{
$connect = mysqli_connect("localhost","root","") or die ("Could not connect");
((bool)mysqli_query($GLOBALS["___mysqli_ston"], "USE login")) or die ("Could not find database");
$query = mysqli_query($GLOBALS["___mysqli_ston"], "SELECT * FROM users WHERE username ='$username'");
$numrows = mysqli_num_rows($query);
if ($numrows !=0)
{
    while ($row =mysqli_fetch_assoc($query))
    {
        $dbusername = $row['username'];
        $dbpassword = $row['password'];
    }
        
    if ($username==$dbusername&&$password==$dbpassword)
    {
        echo header( 'Location: member.php' ) ;
        $_SESSION['username']=$dbusername;
        $_SESSION['userid']=$userid;
    }
    else 
        echo "Inncorrect password";
    
}
else
    die("That user dosen't exist");
}
else
    die("Please enter a username and a password");
?>