参数化SQL查询，优化用户注册PHP代码

在这里对 PHP 非常陌生，我一直在研究如何为我的 SQL 连接使用参数化查询。但是我看到的一切都让我觉得我需要每次更改相同的值才能使用参数化查询。有什么方法可以使用参数化查询来缩小我目前对查询所做的事情吗？我读错了这些东西吗？

我可能是 PHP 的新手，但我知道，总的来说，我知道这段代码非常糟糕。我不喜欢有多个 select * 查询，然后通过关联引用我需要的字段。但是我也遇到了不这样做的问题。有人可以快速浏览一下并把我推向正确的方向吗？我准备被称为哑巴，所以带上它。：） 谢谢。

<?php
    session_start();

    // initializing variables
    $username = "";
    $email    = "";
    $errors = array(); 

    // connect to the database
    $db = mysqli_connect('db_server', 'db_user', 'db_pw', 'db_name');

    // REGISTER USER
    if (isset($_POST['register-submit'])) {
      // receive all input values from the form
      $username = mysqli_real_escape_string($db, $_POST['reg_username']);
      $email = mysqli_real_escape_string($db, $_POST['reg_email']);
      $password_1 = mysqli_real_escape_string($db, $_POST['reg_password_1']);
      $password_2 = mysqli_real_escape_string($db, $_POST['reg_password_2']);
      $actcode  = mysqli_real_escape_string($db, $_POST['reg_actcode']);

      // form validation: ensure that the form is correctly filled ...
      // by adding (array_push()) corresponding error unto $errors array
      if (empty($username)) { array_push($errors, "Username is required"); }
      if (empty($email)) { array_push($errors, "Email is required"); }
      if (empty($password_1)) { array_push($errors, "Password is required"); }
      if ($password_1 != $password_2) { array_push($errors, "The two passwords do not match"); }
      if ($actcode != "tobecaps") { array_push($errors, "Wrong activation code"); }

      // first check the database to make sure 
      // a user does not already exist with the same username and/or email
      $user_check_query = "SELECT * FROM `users` WHERE user_name='$username' OR user_email='$email' LIMIT 1";
      $result = mysqli_query($db, $user_check_query);
      $user = mysqli_fetch_assoc($result);

      if ($user) { // if user exists
        if ($user['user_name'] === $username) {
          array_push($errors, "Username already exists");
        }

        if ($user['user_email'] === $email) {
          array_push($errors, "email already exists");
        }
      }

      // Finally, register user if there are no errors in the form
      if (count($errors) == 0) {
        $password = md5($password_1);//encrypt the password before saving in the database

        $query1 = "INSERT INTO `users` (user_name, user_email, user_password, user_register_time) VALUES('$username', '$email', '$password', 'time()')";
        mysqli_query($db, $query1);

        $query2 = "SELECT * FROM `users` WHERE user_name='$username' LIMIT 1";
        $result2 = mysqli_query($db, $query2);
        $new_user = mysqli_fetch_assoc($result2);
        $user_id = $new_user['user_id'];

        $planet_found = false;

        while (!$planet_found) {
            $galaxy = mt_rand(1, 1);
            $system = mt_rand(1, 15);
            $planet = mt_rand(1, 15);

            $query3 = "SELECT * FROM `planets` WHERE planet_galaxy='$galaxy' AND planet_system='$system' AND planet_planet='$planet' LIMIT 1";
            $result3 = mysqli_query($db, $query3);
            $planet_result = mysqli_fetch_assoc($result3);

            if (!$planet_result) {
                $planet_found = true;
            }
        }

        $query4  = "INSERT INTO `planets` (planet_user_id, planet_galaxy, planet_system, planet_planet) VALUES('$user_id', '$galaxy', '$system', '$planet')";
        $result4 = mysqli_query($db, $query4);

        $query5  = "SELECT * FROM `planets` WHERE planet_user_id='$user_id' LIMIT 1";
        $result5 = mysqli_query($db, $query5);
        $planets_info = mysqli_fetch_assoc($result5);
        $planets_id = $planets_info['planet_id'];

        $query6  = "UPDATE `users` SET user_home_planet_id='$planets_id', user_galaxy='$galaxy', user_system='$system', user_planet='$planet' WHERE user_id='$user_id'";
        $result6 = mysqli_query($db, $query6);

        //update tables with new ids here


        $_SESSION['username']   = $username;
        $_SESSION['success']    = "You are now logged in";
        header("Location: ../");
      } else {
          header("Location: ../");
      }
    }       
?>

是的，这目前正在运行；但我相信我可以打破它。欢迎任何和所有建议。

通常，代码会检查用户是否存在。如果没有，它会将它们添加到用户数据库中，然后创建一个随机位置供它们居住。