无法通过php中的注册表单在我的数据库中插入数据

Question

我是php的新手，所以有人可以帮助我。我试图通过注册表单将数据插入我的数据库。但我不知道为什么我的查询不起作用，有人可以指出我在哪里弄错了。这是代码

$a=$_POST['txt'];
    $b=$_POST['txt1'];
    $c=md5($_POST['pass']);
    $d=md5($_POST['pass1']);
    $f=1;
     $com_code = md5(uniqid(rand()));
    if($_POST['usertype']=='individual')
    {$e=1;
        }
        else if ($_POST['usertype']=='professional')
        {

            $e=2;}
$query="INSERT into user (user_name,user_email,user_password,user_retype_password,user_active,terms_services,unique_code) values ('$a','$b','$c','$d','0','$f','$com_code')";
            $holder1=mysql_query($query,$db_connect) or die ("cannot execute query");
                    if($holder1)
                    {
                        $last_inserted_mysql_id = mysql_insert_id();
                        }
                        $add_to_enrole="INSERT into user_enrole(user_id,user_type_id,user_enrole_active) values ('$last_inserted_mysql_id','$e','1')";
                        $container=mysql_query($add_to_enrole,$db_connect) or die ("cannot insert into user enrole");
        if($container)
  {
   $to = $b;
   $subject = "Confirmation from OnlineShopping to $a";
   $header = "OnlineShopping: Confirmation from OnlineShopping";
   $message = "Please click the link below to verify and activate your account. rn";
   $message .= "http://www.yourname.com/confirm.php?passkey=$com_code";

   $sentmail = mail($to,$subject,$message,$header);

   if($sentmail)
            {
   echo "Your Confirmation link Has Been Sent To Your Email Address.";
   }
   else
         {
    echo "Cannot send Confirmation link to your e-mail address";
   }
  }

我在第一次插入查询时遇到错误，同时将数据插入用户表中，它会在那里死掉。第二个问题是我使用本地主机作为服务器，因此它能够使用本地主机作为服务器发送电子邮件