插入数据库的查询有时有效，有时无效（PHP）

Question

我有一个注册表单，一旦用户为所有字段提供了正确的输入，就应该将填写的信息插入数据库中。每当我测试代码时，信息有时就会成功地插入数据库中，有时甚至不会抛出任何错误。在进行各种测试之后，很难确定是什么原因触发了插入失败，因为它是随机发生的。从数据库中提取的所有登录功能和操作均正常运行。下面显示的是假冒在线商店的代码。我必须对此程序采用面向对象的方法，以便在类函数定义中实现sqli代码。

    httpOptions.headers.set('username', 'password');
    httpOptions.headers.append('Access-Control-Allow-Origin', '*');
    httpOptions.headers.append('Access-Control-Allow-Credentials', 'true');
    httpOptions.headers.append('Access-Control-Allow-Methods', 'GET,POST,OPTIONS');
    this.typesOfDBs = this.http.get<Info[]>(this.ROOT_URL, httpOptions);

以下代码是一个精巧的php文件的一部分，该文件初始化对象并调用函数

    class User
{
  protected $name;
  protected $ID;
  protected $password;
  protected $userName;
  protected $email;
  protected $isAdmin;

  protected function __construct($userName, $password, $email = null, $name = null, $ID = null, $isAdmin = false)
  {
    $this->name = $name;
    $this->ID = $ID;
    $this->password = $password;
    $this->userName = $userName;
    $this->email = $email;
    $this->isAdmin = false;
  }

  public function login(&$usernameError)
  {

    if($userInfo = $this->validateCredentials($usernameError))
    {
      $this->ID = $userInfo['userId'];
      $this->isAdmin = $userInfo['isAdmin'];
      $this->name = $userInfo['name'];
      $this->userName = $userInfo['username'];
      $this->email = $userInfo['email'];
      //$this->password = $userInfo['password'];
      return true;
    }
    else
    {
      return false;
    }

  }

  private function validateCredentials(&$usernameError)
  {
    require "include/login-Database.inc.php";
    $query = "SELECT * FROM users WHERE username = ? or email = ?";
    $stmt = mysqli_stmt_init($conn);

    if (!mysqli_stmt_prepare($stmt, $query))
    {
      echo "SQL error 1";
      exit();
    }
    else
    {
      mysqli_stmt_bind_param($stmt, "ss", $this->userName, $this->userName);
      mysqli_stmt_execute($stmt);
      $resultUser =  mysqli_stmt_get_result($stmt);
      if ($row = mysqli_fetch_assoc($resultUser))
      {
        $checkPassword = password_verify($this->password, $row['password']);
        if (!$checkPassword)
        {
          $usernameError = "password incorrect";
          return null;
        }
        else
        {
          return $row;

        }

      }
      else
      {
        $usernameError = "usernmae is incorrect";
        return null;
      }
    }

  }

  public function logOut()
  {
    if (session_status() == PHP_SESSION_NONE)
    {
        session_start();
    }
    session_unset();
    session_destroy();
  }

}

class Customer extends User
{
  private $phone;
  private $address;

  public function __construct($username, $password, $email = null, $name = null, $address = null, $phone = null)
  {
    $this->phone = $phone;
    $this->address = $address;
    parent::__construct($username, $password, $email, $name);
  }


  public function signUp(&$usernameError, &$emailError)
  {
    require "include/login-Database.inc.php";
    $query1 = "SELECT username FROM users WHERE username = ?";
    $stmt1 = mysqli_stmt_init($conn);

    $query2 = "SELECT username FROM users WHERE email = ?";
    $stmt2 = mysqli_stmt_init($conn);

    if (!mysqli_stmt_prepare($stmt1, $query1) || !mysqli_stmt_prepare($stmt2, $query2))
    {
      $usernameError = "SQL error";
      return false;
    }
    else
    {

      mysqli_stmt_bind_param($stmt1, "s", $this->userName);
      mysqli_stmt_execute($stmt1);
      mysqli_stmt_store_result($stmt1);

      mysqli_stmt_bind_param($stmt2, "s", $this->email);
      mysqli_stmt_execute($stmt2);
      mysqli_stmt_store_result($stmt2);

      $resultUsername = mysqli_stmt_num_rows($stmt1);
      $resultEmail = mysqli_stmt_num_rows($stmt2);
      if($resultUsername > 0 or $resultEmail > 0)
      {
          if ($resultUsername > 0)
          {
              $usernameError = "Username is already taken";

          }
          if ($resultEmail > 0)
          {
              $emailError = "Email is already in use";

          }
          return false;
      }
      else
      {
        //Generate customerId
        $isTaken = true;
        while ($isTaken)
        {
          $customerId = abs( crc32( uniqid() ) );
          $query4 = "SELECT customerId FROM users WHERE customerId = ?";
          $stmt4 = mysqli_stmt_init($conn);
          if (!mysqli_stmt_prepare($stmt4, $query4))
          {
            $usernameError = "SQL error";
            return false;
          }
          else
          {
            mysqli_stmt_bind_param($stmt4, "i", $customerId);
            mysqli_stmt_execute($stmt4);
            mysqli_stmt_store_result($stmt4);
            $resultId = mysqli_stmt_num_rows($stmt4);
            if($resultId == 0)
            {
              $isTaken = false;
            }
          }

        }


        $query5 = "INSERT INTO customers (customerId, customerPhone, customerAddress) VALUES (?,?,?)";
        $stmt5 = mysqli_stmt_init($conn);
        if (!mysqli_stmt_prepare($stmt5, $query5))
        {
          $usernameError = "SQL error";
          return false;

        }
        else
        {
          mysqli_stmt_bind_param($stmt5, "iss", $customerId, $this->phone, $this->address);
          mysqli_stmt_execute($stmt5);
        }


        $query3 = "INSERT INTO users (userId, adminId, customerId, username, name, email, password, isAdmin) VALUES (?, ?, ?, ?, ?, ?, ?, ?)";
        $stmt3 = mysqli_stmt_init($conn);
        if (!mysqli_stmt_prepare($stmt3, $query3))
        {
          $usernameError = "SQL error";
          return false;
        }
        else
        {
          $username = $this->userName;
          $name = $this->name;
          $email = $this->email;
          $notAdmin = 0;
          $noAdminId = null;
          $pass = password_hash($this->password, PASSWORD_DEFAULT);
          mysqli_stmt_bind_param($stmt3, "iiissssi", $customerId, $noAdminId, $customerId ,$username, $name, $email, $pass,  $notAdmin);
          mysqli_stmt_execute($stmt3);
          return true;
        }


      }
    }

  }

以下两个图像是用户表和客户表的结构。

User Table

Customer Table

让我知道你们的想法。谢谢。