Connect two drop down menu whit Mysqli - mysqli

Question

I have this two drop down menu , they get values from Mysqli data base
firs menu for company name second one for project of company
I want when i select company from first menu , just that project appear on second menu of that company i selected
<form id="company" name="company" method="post" action="">
<label for="company"></label>
<select name="company" id="company">
<?php
$cmpsql="SELECT * FROM company ";
$cmpresult=mysqli_query($mng,$cmpsql);
$row_cmp=mysqli_fetch_assoc($cmpresult);
do {
?>
<option value="<?php echo $row_cmp['company'] ?>"><?php echo $row_cmp['company'] ?></option>
<?php } while ($row_cmp= mysqli_fetch_assoc($cmpresult))?>
</select>
<label for="project"></label>
<select name="project" id="project">
<?php
$psql="SELECT * FROM project ";
$presult=mysqli_query($mng,$psql);
$row_p=mysqli_fetch_assoc($presult);
do {
?>
<option value="<?php echo $row_p['project'] ?>"><?php echo $row_p['project'] ?></option>
<?php } while ($row_p= mysqli_fetch_assoc($presult)) ?>
</select>
</form>

Answer 1

I solved my problem
index page
<script src="style/jquery.js"></script>
<script>
function getid(val){
$.ajax({
type :"POST",
url : "getdata.php",
data :"cid="+val,
success:function(data){
$("#proje").html(data);
}})}
</script>
<form id="company" name="company" method="post" action="">
<label for="company">Company</label>
<select name="company" id="company" onchange="getid(this.value)">
<?php
$cmpsql="SELECT * FROM company ";
$cmpresult=mysqli_query($mng,$cmpsql);
$row_cmp=mysqli_fetch_assoc($cmpresult);
do {
?>
<option value="<?php echo $row_cmp['company'] ?>"><?php echo $row_cmp['company'] ?></option>
<?php } while ($row_cmp= mysqli_fetch_assoc($cmpresult))?>
</select>
<label for="project">Project</label>
<select name="project" id="proje">
<option value="">Choose Company First</option>
</select>
</form>
getdata.php page
<?php require_once('Connections/mng.php');
mysqli_select_db($mng, "management") or die("cannot select DB");
$cid=$_POST['cid'];
$psql="SELECT * FROM project WHERE company='$cid' ";
$presult=mysqli_query($mng,$psql);
$row_p=mysqli_fetch_assoc($presult);
do {
?>
<option value="<?php echo $row_p['project'] ?>"><?php echo $row_p['project'] ?></option>
<?php } while ($row_p= mysqli_fetch_assoc($presult)) ?>