问提交时重新加载PHP登录

EN

    <?php
    include 'Database/connect.php';

?>
<?php

$username= $_POST['user'];
$password= hash("sha256", $_POST['pass']);

   $statement = $db->prepare('SELECT * FROM User WHERE username=? AND password=?');
   $statement->bindValue(1, $username);
   $statement->bindValue(2, $password);
   $result = $statement->execute();

if(isset($username) && isset($password)){
   if(empty($result->fetchArray(SQLITE3_ASSOC))){
       echo "<script>alert('Invalid Credentials')</script>";
       }
   else{
       session_start();
       $_SESSION['user'] = $username;
       $random = md5(rand(1,1000)); //encoded with md5, avoid bad string output.
       setcookie($username, $random, time()+3600);
       header("Location: Blog/home.php");
       }
   }

?>
<form action='index.php' method="POST">
                            <input type="email" id="exampleInputEmail1" class="form-control" id="user"
                                placeholder="Email" style="margin-bottom:1vw;">
                            <input type="password" id="exampleInputPassword1" class="form-control" id="pass"
                                placeholder="Password" style="margin-bottom:1vw;">
                            <input type="checkbox" required id="privacypolicycheckbox" name="privacypolicycheckbox"
                                value="check">
                            <label for="privacypolicycheckbox">I have read and agreed to the <a style="color:blue; "
                                    onclick="myFunction()">policy
                                    documents</a></label><br>
                            <input type="submit" class="btn btn-block btn-danger" value="Log In" name="sumbit-btn">
                        </form>