ช่วยดูโค้ดการเช็คค่าซ้ำของรหัส โดยใช้ Java script

$in = " INSERT INTO drb_product(drb_pd_code , drb_cg_id) 
           VALUES('GL-ES-$drb_cg_id$drb_pd_code' , '$drb_cg_id' )";

<!------ Check Code ซ้ำ ------->
	<script type="text/javascript" src="jquery-1.2.6.min.js"></script>
	<link rel="stylesheet" type="text/css" href="style_c.css" />
	<SCRIPT type="text/javascript">
	pic1 = new Image(16, 16); 
	pic1.src = "loader.gif";

	$(document).ready(function()
	{
		$("#drb_pd_code").change(function() 
		{ 
			var pd_code = $("#drb_pd_code").val();
                    <--! อันนี้ที่ลองสร้างตัวแปรมั่วๆดู ก็ใส่ดื้อๆไปเลย แต่ยังทำไม่ได้
			var cg_id = $("#drb_cg_id").val();
			var str_c = "ES-";
			var str_ce = "-";  -->

			if(pd_code.length >= 3)
			{
				$("#status").html('<img src="loader.gif" align="absmiddle">&nbsp;Checking availability...');
				$.ajax(
				{   
					type: "POST", url: "check.php", data: "drb_pd_code="+ pd_code, 
				 
    				success: function(msg)
					{  
   						$("#status").ajaxComplete(function(event, request, settings)
						{ 
							if(msg == 'OK')
							{ 
        						$("#drb_pd_code").removeClass('object_error'); // if necessary
								$("#drb_pd_code").addClass("object_ok");
								$(this).html('&nbsp;<img src="tick.gif" align="absmiddle">');
							}  
							else  
							{  
								$("#drb_pd_code").removeClass('object_ok'); // if necessary
								$("#drb_pd_code").addClass("object_error");
								$(this).html(msg);
								alert("รหัสนี้ใช้งานแล้ว");
							}
  					 	});
				 	} 
				}); 
			}
			else
			{
				$("#status").html('<font color="red">คุณระบุรหัสต่ำกว่า <strong>3</strong> ตัว!</font>');
				$("#drb_pd_code").removeClass('object_ok'); // if necessary
				$("#drb_pd_code").addClass("object_error");
			}
		});
	});
	</SCRIPT><!----- End Check Code ซ้ำ ----->