php变量不更新

 $exists = 0;
    $result = $mysqli->query("SELECT username from tblUsers WHERE username = '$username'");
    if ($result->num_rows == 1) {
      $exists = 1;
      $result = $mysqli->query("SELECT email from tblUsers WHERE email = '$email'");
      if ($result->num_rows == 1)  {
$exists = 2;
}
    } 
else {
      $result = $mysqli->query("SELECT email from tblUsers WHERE email = '{$email}'");
      if ($result->num_rows == 1) {
$exists = 3;
}
    }

     if ($exists == 1) echo "<p>Username already exists!</p>";
    else if ($exists == 2) echo "<p>Username and Email already exists!</p>";
    else if ($exists == 3) echo "<p>Email already exists!</p>";
    else {
     // insert data into mysql database
}

我已经为自己的想法进行了略微的重新编写，但是我最初的想法是，对于OO编程，您正在使用将数据输入数据库的过程方式，该如何做：

   $exists = 0;
        if($object_Var = $mysqli->prepare("SELECT username from tblUsers WHERE username = ?")) {
        $object_Var->bind_param("s",$username);
        $object_Var->execute();
     }
        else {
        ///this will run if the script execution failes for whatever reason
        print "error: ".$mysqli->error;
        } 
  if ($object_Var->num_rows == 1) {
           $exists = 1;
           $object_Var_two = $mysqli->prepare("SELECT email from tblUsers WHERE email = ?");
           $object_Var_two->bind_param("s",$email);
           $object_Var_two->execute();
          if ($object_Var_two->num_rows == 1)  {
                $exists = 2;
            }
        } 
    else {
          $object_Var_three = $mysqli->prepare("SELECT email from tblUsers WHERE email = ?");
          $object_Var_three->bind_param("s",$email);
          $object_Var_three->execute();
          if ($object_Var_three->num_rows == 1) {
               $exists = 3;
            }
        }

         if ($exists == 1) {
            echo "<p>Username already exists!</p>";
         }
        elseif ($exists == 2) {
            echo "<p>Username and Email already exists!</p>";
            }
        elseif ($exists == 3) {
            echo "<p>Email already exists!</p>";
            }
        else {
         // insert data into mysql database
        }

等等等

抱歉，我没有完成全部脚本，但我认为将OO方法与OO MySQLi界面一起使用应该会有所帮助。还将die();语句添加到各行中，以查看代码到达的位置以进行调试。

我认为添加语句是否成功执行MySQL中的检查是明智的。