PHP page not returning value - php

Question

I am trying to retrieve a value from a database through ajax and php.
The ajax code is as follows:
<script>
$(document).ready(function() {
$("#buyprice").change(function() {
if ($("#sname").val() == "") {
alert("Enter Stock name.");
} else {
var sn = $("#sname").val();
alert(sn);
if (window.XMLHttpRequest) {// code for IE7+, Firefox, Chrome, Opera, Safari
xmlhttp = new XMLHttpRequest();
}
xmlhttp.onreadystatechange = function() {
if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {
var x = xmlhttp.responseText;
};
};
xmlhttp.open("GET", "getstockprice.php?q="+sn, true);
xmlhttp.send();
alert("here");
};
alert("here");
var bp = $("#buyprice").val();
alert(bp);
alert(x.val());
if(bp>(1.1*x)||bp<(1.1*x)){
alert("Price violating 10% constraint.");
}
alert("here");
});
});
</script>
The php page is as follows:
<?php
$q = $_GET['q'];
$con = mysqli_connect('localhost','root','','stock_market');
if (!$con)
{
die('Could not connect: ' . mysqli_error($con));
}
mysqli_select_db($con,"ajax_demo");
$sql="SELECT stock_price FROM live_prices WHERE stock_name = '".$q."'";
$result = mysqli_query($con,$sql);
$row = mysqli_fetch_array($result);
mysqli_close($con);
?>
Can someone please tell me where I am going wrong.

Answer 1

you should use echo or return to return something from php.
<script>
$(document).ready(function() {
$("#buyprice").change(function() {
if ($("#sname").val() == "") {
alert("Enter Stock name.");
} else {
var sn = $("#sname").val();
alert(sn);
if (window.XMLHttpRequest) {// code for IE7+, Firefox, Chrome, Opera, Safari
xmlhttp = new XMLHttpRequest();
}
xmlhttp.onreadystatechange = function() {
if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {
var x = xmlhttp.responseText;
};
};
xmlhttp.open("GET", "getstockprice.php?q="+sn, true);
xmlhttp.send();
alert("here");
};
alert("here");
var bp = $("#buyprice").val();
alert(bp);
alert(x);
if(bp>(1.1*x)||bp<(1.1*x)){
alert("Price violating 10% constraint.");
}
alert("here");
});
});
</script>
PHP
<?php
$q = $_GET['q'];
$con = mysqli_connect('localhost','root','','stock_market');
if (!$con)
{
die('Could not connect: ' . mysqli_error($con));
}
mysqli_select_db($con,"ajax_demo");
$sql="SELECT stock_price FROM live_prices WHERE stock_name = '".$q."'";
$result = mysqli_query($con,$sql);
$row = mysqli_fetch_array($result);
mysqli_close($con);
echo $row['stock_price'];
?>

Answer 2

The php script needs to echo the value. This does not display the value on your page, it merely makes the value avalailble to the javascript.
I would suggest using jquery and use the built in ajax functionality. This works much easier.
See the jquery ajax page, and an example straight from there:
$.ajax({
type: "POST",
url: "some.php",
data: { name: "John", location: "Boston" }
}).done(function( msg ) {
alert( "Data Saved: " + msg );
});