Check field value is already exists in mysql database with php and ajax

 <script type="text/javascript">
  //function to create ajax object
  function pullAjax(){
    var a;
    try{
      a=new XMLHttpRequest()
    }
    catch(b)
    {
      try
      {
        a=new ActiveXObject("Msxml2.XMLHTTP")
      }catch(b)
      {
        try
        {
          a=new ActiveXObject("Microsoft.XMLHTTP")
        }
        catch(b)
        {
          alert("Your browser broke!");return false
        }
      }
    }
    return a;
  }

  function validate()
  {
    site_root = '';
    var x = document.getElementById('stickerno');
    var msg = document.getElementById('msg');
    user = x.value;

    code = '';
    message = '';
    obj=pullAjax();
    obj.onreadystatechange=function()
    {
      if(obj.readyState==4)
      {
        eval("result = "+obj.responseText);
        code = result['code'];
        message = result['result'];

        if(code==0)
        {
          x.style.border = "1px solid red";
          msg.style.color = "red";
        }
        else
        {
          x.style.border = "1px solid #000";
          msg.style.color = "green";
        }
        msg.innerHTML = message;
      }
    }
    obj.open("GET",site_root+"validate.php?username="+user,true);
    obj.send(null);
  }
</script>
 <style>
#stickerno{border: 1px solid #000;}
</style>


 <th>Sticker No.</th> <th scope="row"><input type="text" name="stickerno" value="<?=$raj['stickerno']?>" id="stickerno"  onchange="validate();"/><div id="msg"></div></th>


validate.php


<?php
 include("config.php");
$stickerno = strip_tags(trim($_REQUEST['username']));

// Query database to check if the username is available
$query = mysql_query("Select * from wp_proitem where stickerno ='$stickerno' ");
$ct=mysql_num_rows($query);
// Execute the above query using your own script and if it return you the
// result (row) we should return negative, else a success message.
 if($ct>0)
 {
echo json_encode(array('code'  =>  0,'result'  =>  "Sticker No.# $stickerno is already exist.<input type='hidden' name='stickid' value='1' id='stickid'>"));

 }
 else
 {

  echo  json_encode(array('code'  =>  1,'result'  => "Sticker No.# $stickerno is  available<input type='hidden' name='stickid' value='0' id='stickid'>"));
 
 }


?>


after that check validate using javascript

else if(document.formtest.stickerno.value=="")
    {
        alert("Please Enter the Sticker No");
            document.formtest.stickerno.focus();
        return false;
    }
   
    else if(document.formtest.stickid.value=="1")
    {
        alert("Please Enter the  Correct Sticker No");
            ///document.formtest1.stickerno.focus();
        return false;
    }