การบันทึกข้อมูลแบบ ajax ครับคือผมงงตรงที่ว่าทำไมค่าตัวปรมันไม่ลงฐานข้อมูลครับ

<script language="JavaScript">
	   var HttPRequest = false;

	   function doCallAjax(Mode) {
		  HttPRequest = false;
		  if (window.XMLHttpRequest) { // Mozilla, Safari,...
			 HttPRequest = new XMLHttpRequest();
			 if (HttPRequest.overrideMimeType) {
				HttPRequest.overrideMimeType('text/html');
			 }
		  } else if (window.ActiveXObject) { // IE
			 try {
				HttPRequest = new ActiveXObject("Msxml2.XMLHTTP");
			 } catch (e) {
				try {
				   HttPRequest = new ActiveXObject("Microsoft.XMLHTTP");
				} catch (e) {}
			 }
		  } 
		  
		  if (!HttPRequest) {
			 alert('Cannot create XMLHTTP instance');
			 return false;
		  }
	
		  var url = 'save_reply.php';
		  var pmeters = "&tdetail=" + encodeURI( document.getElementById("detail").value) +
						"&tuse=" + encodeURI( document.getElementById("use").value ) +
						"&temail=" + encodeURI( document.getElementById("email").value ) +
						"&tp=" + encodeURI( document.getElementById("p").value ) +
						"&tMode=" + Mode;

			HttPRequest.open('POST',url,true);

			HttPRequest.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
			HttPRequest.setRequestHeader("Content-length", pmeters.length);
			HttPRequest.setRequestHeader("Connection", "close");
			HttPRequest.send(pmeters);
			
			
			HttPRequest.onreadystatechange = function()
			{

				 if(HttPRequest.readyState == 3)  // Loading Request
				  {
				   document.getElementById("mySpan").innerHTML = "Now is Loading...";
				  }

				 if(HttPRequest.readyState == 4) // Return Request
				  {
				   document.getElementById("mySpan").innerHTML = HttPRequest.responseText;
				   document.getElementById("detail").value = '';
				   document.getElementById("use").value = '';
				   document.getElementById("email").value = '';
				   document.getElementById("p").value ='$pid';
				   
				  }
				
			}

	   }
	</script>



<form name="frmMain" id="frmMain">
<div class="bg2"><font class="white">RE.แสดงความคิดเห็น</font></div>
<div class="bg1">
<table  height="95"width="464">
  <tr>
  <td width="94" height="39" align="left"><font class="yellow"> - Comment ** </font></td>
  <td width="358" align="left"><textarea name="detail" cols="35" id="detail"></textarea></td>
  <tr>
    <td height="23" align="left"><font class="yellow">- Username ** </font></td>
    <td align="left"><input name="use" type="text" id="use" size="40" /></td>
  <tr>
    <td height="23" align="left"><font class="yellow">- Email address **</font></td>
    <td align="left"><input name="email" type="text" id="email" size="40" />
      <input name="btn" type="button" id="Submit" value="comment" onclick="javascript:doCallAjax('ADD');" />
      <span class="b1">
      <input name="p" type="hidden" id="p" value="<?=$pid?>" />
      </span> </td>
  </table>
</div>
<span id="mySpan"></span>
</form>

$strMode = $_POST["tMode"];
$pid=$_REQUEST['tp'];
$detail=$_POST['tdetail'];
$use=$_POST['tuse'];
$email=$_POST['temail'];
$date=date("Y-m-d H:i:s");


 
$sql1="update tb_post set p_post=p_post +1   where p_id='$pid' ";
$result1=mysql_query($sql1);

$sql2="update tb_post set p_status='a',user_post='Guest'  where p_id='$pid' ";
$result2=mysql_query($sql2);



////--------------------เก็บรหัสสินค้าเป็นรหัส------------------************

 if($strMode == "ADD"){


$sql = "SELECT r_id FROM tb_reply  ORDER BY  r_id DESC LIMIT 1";
$result = mysql_query($sql);
      if(mysql_num_rows($result) > 0)
      {
           $row = mysql_fetch_array($result);
           sscanf($row[0] ,"0%d" , $id); 
		   $id++;
 
 $sql = "INSERT INTO tb_reply VALUES(CONCAT('0',RIGHT(CONCAT('0000' , $id) , 4)),'$detail','$use','$email','$date','$pid')"; 		   
      }
      else
      {
	  
 
 $sql = "INSERT INTO tb_reply VALUES('00001','$detail','$use','$email','$date','$pid')";
      }

} 
 
 mysql_query($sql);