如何使php中的SQLi易受攻击登录

我的任务是制作一个易受攻击的php应用程序，这是我的登录页面代码。问题是我不能让它变得脆弱。当我尝试使用登录字段进行SQL注入时，不会发生任何事情。

如何使其易受SQLi攻击、or '1'='1'或类似攻击？

checklogin.php

require "config.php";
$tbl_name="members"; 
mysql_connect("$servername", "$dbusername", "$dbpassword")or die("Spajanje bezuspješno");
mysql_select_db("$dbname")or die("Selektrianje baze bezuspješno");
$myusername=$_POST['myusername'];
$mypassword=$_POST['mypassword'];
$sql="SELECT * FROM $tbl_name WHERE username='$myusername' and password='$mypassword'";
$result=mysql_query($sql);
$count=mysql_num_rows($result);
if($count==1){
  $_SESSION['myusername'] = $myusername;
  $_SESSION['mypassword'] = $mypassword;
  header("location:addnews.php");
}
else {
  header("location:login_failed.php"); 
}

config.php

$servername='localhost';    
$dbusername='root';                
$dbpassword='qwe123';               
$dbname='ferida';     
connecttodb($servername,$dbname,$dbusername,$dbpassword);
function connecttodb($servername,$dbname,$dbusername,$dbpassword)
{
  global $link;
  $link=mysql_connect ("$servername","$dbusername","$dbpassword");
  if(!$link){die("Ne mogu se spojiti na MySQL");}
  mysql_select_db("$dbname",$link) or die ("Ne mogu otvoriti bazu podataka".mysql_error());
}

数据库

CREATE TABLE IF NOT EXISTS `members` (
  `id` int(4) NOT NULL AUTO_INCREMENT,
  `username` varchar(65) NOT NULL,
  `password` varchar(65) NOT NULL,
  PRIMARY KEY (`id`)
) 
ENGINE=MyISAM  DEFAULT CHARSET=utf8 AUTO_INCREMENT=4*/ ;
INSERT INTO `members` (`id`, `username`, `password`) VALUES
(1, 'admin', 'P@ssw0rd'),
(2, 'r00t', '1qa2ws'),
(3, 'editor', 'q1w2e3r4');