I just want to insert the value or the name of PROVINCE, CITY and BARANGAY to the database. I'm new in PHP i'm a little confused about this one.
PHP
    <?php
    session_start();
    $link=mysqli_connect("localhost","root","");
mysqli_select_db($link,"mknr2");
    if(isset($_POST['submit'])){
    $province = $_POST['province'];
    $city = $_POST['city'];
    $barangay = $_POST['barangay'];
    $sql = "INSERT INTO users(PROVINCE, CITY, BARANGAY) VALUES ('$province','$city','$barangay')";
    if($link->query($sql) === TRUE){
        echo "Sent!";
    }
    else{
        echo "Error:" . $sql . "<br>" . $link->error;
    }
}
?>
HTML
<h2 style="font-size:20px;font-weight:bolder;font-family:arial;margin-left:2%;">Address</h2>
<!--  PROVINCE -->
    <select id="provincedd" name="province" onchange="change_province()" class="province">
        <option>Select</option>
        <?php
            $res=mysqli_query($link,"select * from province");
                while($row=mysqli_fetch_array($res)) {
            ?>
            <option value="<?php echo $row["id"]; ?>"><?php echo $row["name"]; ?></option>
            <?php } ?>
    </select>   
<!--  PROVINCE -->
    <select id="city" name="city" class="city">
            <option>Select</option>     
    </select>
    <select id="barangay" name="barangay" class="barangay">
            <option>Select</option>
    </select>
AJAX.php
<?php
$link=mysqli_connect("localhost","root","");
mysqli_select_db($link,"mknr2");
if(isset($_GET["province"]))
{
$province=$_GET["province"];
        $res=mysqli_query($link,"select * from city where province_id=$province");
        echo "<select id='citydd' onchange='change_city()'>";
        echo "<option>"; echo "Select"; echo "</option>";
        while($row=mysqli_fetch_array($res))
        {
        echo "<option value='$row[id]' selected >"; echo $row["name"]; echo "</option>";
        }
        echo "</select>";
}
if(isset($_GET["city"]))
{
    $city=$_GET["city"];
        $res=mysqli_query($link,"select * from barangay where city_id=$city");
        echo "<select>";
        echo "<option>"; echo "Select"; echo "</option>";
        while($row=mysqli_fetch_array($res))
        {
        echo "<option value='$row[id]' selected>"; echo $row["name"]; echo "</option>";
        }
        echo "</select>";
}
?>
JAVASCRIPT
<script type="text/javascript">
function change_province()
{
var xmlhttp=new XMLHttpRequest();
xmlhttp.open("GET","ajax.php?province="+document.getElementById("provincedd").value,false);
xmlhttp.send(null);
city.style.display = "block";
document.getElementById("city").innerHTML=xmlhttp.responseText;
 if(document.getElementById("provincedd").value=="Select")
 {
 document.getElementById("barangay").innerHTML="<select><option>Select</option></select>";
 }
}
function change_city()
{
var xmlhttp=new XMLHttpRequest();
xmlhttp.open("GET","ajax.php?city="+document.getElementById("citydd").value,false);
xmlhttp.send(null);
document.getElementById("barangay").innerHTML=xmlhttp.responseText;
}
</script>
 
     
    