Hi i am new in php javascript. Firstly sorry for the long post. i am having 3 sets of drop down list. i am trying to display the table when i selected the last dropdown list. all example are shows for only one dropdown only. Help are really appreciated!! Thanks in advance. 
here is my javascript code
<script type= "text/javascript">
function ajaxFunction(choice)
{
var httpxml;
try
{
httpxml=new XMLHttpRequest();
}
catch (e)
{
try
{
httpxml=new ActiveXObject("Msxml2.XMLHTTP");
}
catch (e)
{
try
{
httpxml=new ActiveXObject("Microsoft.XMLHTTP");
}
catch (e)
{
alert("Your browser does not support AJAX!");
return false;
}
}
}
function stateChanged()
{
if(httpxml.readyState==4)
{
var myObject = JSON.parse(httpxml.responseText); //received the data
for(j=document.myForm.PTT.options.length-1; j>=0; j--)
{
document.myForm.PTT.remove(j);
}
var PTT1=myObject.value.PTT1;
var optn = document.createElement("OPTION");
optn.text = 'Select PTT';
optn.value = '';
document.myForm.PTT.options.add(optn);
for (i=0; i<myObject.PTT.length; i++)
{
var optn = document.createElement("OPTION");
optn.text = myObject.PTT[i];
optn.value = myObject.PTT[i];
document.myForm.PTT.options.add(optn);
if(optn.value==PTT1)
{
var k = i+1;
document.myForm.PTT.options[k].selected=true;
//document.myForm.PTT.options[i].selected= true;
}
}
for (j=document.myForm.EXT.options.length-1; j>=0; j--)
{
document.myForm.EXT.remove(j);
}
var EXT1=myObject.value.EXT1; // this one is the problem cause. forgot to add value.
for (i=0; i<myObject.EXT.length; i++)
{
var optn = document.createElement("OPTION");
optn.text = myObject.EXT[i];
optn.value = myObject.EXT[i];
document.myForm.EXT.options.add(optn);
if(optn.value==EXT1)
{
var h = i+1;
document.myForm.EXT.options[i].selected=true;
}
}
//document.getElementById("txtHint").style.background='#00f040';
document.getElementById("txtHint").innerHTML = httpxml.responseText;
}
}
var url="checking2.php";
var REGION=myForm.REGION.value;
if(choice != 's1')
{
var PTT=myForm.PTT.value;
var EXT=myForm.EXT.value;
}
else{
var PTT = '';
var EXT = '';
}
url=url+"?REGION="+REGION; // all this three will temporary store the selection values.
url=url+"&PTT="+PTT;
url=url+"&EXT="+EXT;
myForm.st.value=PTT; //why is this needed.
/*
var message=myObject.value.message;
var bgcolor=myObject.value.bgcolor;
///////////////////////////////////
var str="<table width='200' align=center>";
for(i=0;i<myObject.data.length;i++)
{
str = str + "<tr bgcolor='#f1f1f1'><td >ID:</td><td>" + myObject.data[i].ID + " </td></tr>";
str = str + "<tr ><td >REGION</td><td>" + myObject.data[i].REGION + " </td></tr>";
str = str + "<tr bgcolor='#f1f1f1'><td>EXT</td><td>"+ myObject.data[i].EXT + "</td></tr>";
str = str + "<tr><td>PTT</td><td>"+ myObject.data[i].PTT + "</td></tr>";
}
str = str + "</table>" ;
document.getElementById("display").innerHTML=str;
////////////////////////////////////*/
document.getElementById("txtHint2").innerHTML = url; //this will display the selection output.
httpxml.onreadystatechange=stateChanged;
httpxml.open("GET",url,true);
httpxml.send(null);
//document.getElementById("txtHint").innerHTML="Please Wait...";
//document.getElementById("txtHint").style.background='#f1f1f1';
}
</script>
here, where i can make the selection.
<form name="myForm" method='POST' action='details2.php'>
<input type=hidden name=st value=0>
<table width= 1000>
<tr><td>
<label>Select Region :</label><select name=REGION id='s1' onchange=ajaxFunction('s1');>
<option value=''>Select One</option>
<?php
include "config2.php";
$sql="SELECT DISTINCT REGION FROM all_exchangelist";
foreach ($dbo->query($sql)as $row)
{
echo "<option value= $row[REGION]>$row[REGION]</option>";
}
?>
</select>
</td><td><label>Select PTT :</label><select name=PTT onchange=ajaxFunction('s2');>
<option value=''>Select One</option>
</select></td>
<td><label>Select Exchange:</label><select name=EXT onchange="ajaxFunction(this.value)";>
<option value=''>Select One</option>
</select></td>
</tr></tr>
<tr><td colspan=3><input type=submit value='Submit'></td></tr>
</form>
</table>
<br>
<br>
<div id="txtHint2"></div>
this code are to check the validation of selection form.
<?php
include "config2.php";
error_reporting(0);
$REGION=$_GET['REGION'];
$PTT1=$_GET['PTT'];
$EXT1=$_GET['EXT'];
/*if((strlen($REGION))) > 0 and (!ctype_alpha($REGION)))
{
echo "Data Error";
exit;
}
if((strlen($PTT1)) > 0 and ctype_alpha(str_replace(' ', '', $PTT1)) === false)
{
echo "Data Error";
exit;
}*/
if(strlen($REGION) > 0)
{
$q_REGION= "Select distinct PTT from all_exchangelist where REGION = '$REGION' ";
}
else {
$q_REGION= "Select PTT from all_exchangelist";
}
$sth = $dbo->prepare($q_REGION);
$sth->execute();
$PTT = $sth->fetchAll(PDO::FETCH_COLUMN);
$q_PTT="Select distinct EXT from all_exchangelist where ";
if(strlen($REGION) > 0)
{
$q_PTT = $q_PTT . " REGION = '$REGION' ";
}
if(strlen($PTT1) > 0)
{
$q_PTT= $q_PTT . " and PTT= '$PTT1'";
}
$sth = $dbo->prepare($q_PTT);
$sth->execute();
$EXT = $sth->fetchAll(PDO::FETCH_COLUMN);
/*
//////////
$sql="select * from all_exchangelist where";
$row=$dbo->prepare($sql);
$row->execute();
$result=$row->fetchAll(PDO::FETCH_ASSOC);
/////////*/
$main = array('PTT'=>$PTT, 'EXT'=>$EXT, 'value'=>array("PTT1"=>"$PTT1", "EXT1"=>"$EXT1"));
echo json_encode($main);
?>
this one will display all the selection url.
<body>
<?php
include "config2.php";
include 'trying2.php';
echo "Region : $_POST[REGION] <br>
Ptt : $_POST[PTT]<br>
Ext : $_POST[EXT]<br>
<br>
<br>
Return to <a href=trying2.php>Selection Page</a>";
?>