php if isset _POST username isset _POST login connect mysql_connect lo

<?php
if(isset($_POST['username']) && isset($_POST['login'])){
 $connect= mysql_connect("localhost","root") or die(mysql_error());
    mysql_select_db("register");
       $username=$_POST['username'];
	   $login=$_POST['login'];
	   $password=$_POST['password'];
	   $r_password=$_POST['r_password'];
	  if($password==$r_password) {  
	  die("<h1>Registration is successful<h1>");
	
		$query=mysql_query("INSERT INTO users (`username`, `login`, `password`) VALUES('$username', '$login', '$password')")or die(mysql_error());

	   
	    }
	   else{
	     die("<h1>Password must match<h1>");
		 }
	   }
	   if (isset($_POST['enter'])){
		   $e_login=$_POST['e_login'];
		   $e_password=$POST['e_password'];
		   
		   $query=mysql_query("SELECT * FROM users WHERE login='$e_login");
		   $user_data=mysql_fetch_array($query);
		   if($user_data['password'] == $e_password){
		   
			 echo "osdfgk";
		   }
		   
		   else{
			 echo"wrong password or login";
			 }
       }
	   ?>

<form method="post" action ="register.php">
  <input type="text"name="username" placeholder="Username" required /><br>
  <input type="text"name="login"placeholder="Login" required  /> <br>
  <input type="password"name="password"placeholder="Password" required /> <br>
  <input type="password"name="r_password"placeholder="Repeat password" required /> <br>
  <input type="submit" name="submit" value="register"/>
</form>

  <form method="post" action ="register.php">
     <input type="text"name="e_login"placeholder="Login" required  /> <br>
    <input type="password"name="e_password"placeholder="Password" required /> <br>
    <input type="submit" name="enter" value="Enter"/>
  </form>