ผมสร้างระบบ Login และ CRUD แบบง่าย ๆ ด้วย PHP + Bootstrap 5
(โปรเจกต์เริ่มต้นสำหรับมือใหม่)

CREATE TABLE users (
  id INT AUTO_INCREMENT PRIMARY KEY,
  username VARCHAR(50) NOT NULL UNIQUE,
  password VARCHAR(255) NOT NULL
);

CREATE TABLE students (
  id INT AUTO_INCREMENT PRIMARY KEY,
  name VARCHAR(100) NOT NULL,
  class VARCHAR(20) NOT NULL,
  marks INT NOT NULL
);

<?php
mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT);

define('DB_HOST', 'localhost');
define('DB_USER', 'root');
define('DB_PASS', '');
define('DB_NAME', 'pcm_demo');

try {
    $conn = new mysqli(DB_HOST, DB_USER, DB_PASS, DB_NAME);
    $conn->set_charset('utf8mb4');
} catch (mysqli_sql_exception $e) {
    die('Connection failed: ' . $e->getMessage());
}

<?php
require 'config/db.php';

if ($_SERVER['REQUEST_METHOD'] === 'POST') {
    $username = trim($_POST['username']);
    $hashed   = password_hash($_POST['password'], PASSWORD_DEFAULT);

    $stmt = $conn->prepare("INSERT INTO users (username, password) VALUES (?, ?)");
    $stmt->bind_param("ss", $username, $hashed);
    $stmt->execute();

    header('Location: login.php?registered=1');
    exit;
}

<?php
session_start();
require 'config/db.php';
$error = null;

if ($_SERVER['REQUEST_METHOD'] === 'POST') {
    $username = trim($_POST['username']);
    $password = $_POST['password'];

    $stmt = $conn->prepare("SELECT id, password FROM users WHERE username = ?");
    $stmt->bind_param("s", $username);
    $stmt->execute();
    $result = $stmt->get_result();
    $user   = $result->fetch_assoc();

    if ($user && password_verify($password, $user['password'])) {
        session_regenerate_id(true);
        $_SESSION['user_id']  = $user['id'];
        $_SESSION['username'] = $username;
        header('Location: students.php');
        exit;
    }
    $error = 'Username หรือ Password ไม่ถูกต้อง';
}

<div class="container mt-5" style="max-width:400px">
  <h3 class="mb-4">เข้าสู่ระบบ</h3>
  <?php if ($error): ?>
    <div class="alert alert-danger"><?= htmlspecialchars($error) ?></div>
  <?php endif; ?>
  <form method="post">
    <input name="username" class="form-control mb-3" placeholder="Username" required>
    <input type="password" name="password" class="form-control mb-3" placeholder="Password" required>
    <button class="btn btn-primary w-100">เข้าสู่ระบบ</button>
  </form>
</div>

<?php
session_start();
if (!isset($_SESSION['user_id'])) {
    header('Location: login.php');
    exit;
}
require 'config/db.php';
$students = $conn->query("SELECT * FROM students ORDER BY id DESC");
?>
<table class="table table-striped">
  <tr><th>ชื่อ</th><th>ห้อง</th><th>คะแนน</th><th></th></tr>
  <?php while ($row = $students->fetch_assoc()): ?>
  <tr>
    <td><?= htmlspecialchars($row['name']) ?></td>
    <td><?= htmlspecialchars($row['class']) ?></td>
    <td><?= $row['marks'] ?></td>
    <td>
      <a href="edit.php?id=<?= $row['id'] ?>" class="btn btn-sm btn-warning">แก้ไข</a>
      <a href="delete.php?id=<?= $row['id'] ?>" class="btn btn-sm btn-danger"
         onclick="return confirm('ลบรายการนี้?')">ลบ</a>
    </td>
  </tr>
  <?php endwhile; ?>
</table>

<?php
session_start();
if (!isset($_SESSION['user_id'])) { header('Location: login.php'); exit; }
require 'config/db.php';

$id = (int) ($_GET['id'] ?? 0);
$stmt = $conn->prepare("DELETE FROM students WHERE id = ?");
$stmt->bind_param("i", $id);
$stmt->execute();

header('Location: students.php');
exit;