SQL Insert won't insert on all fields - php

Question

I have PHP generating an HTML form and I'm trying to write a script that will update the information in the database. For some reason it works on some of the fields and not others.
Code which won't work:
PHP-Form that users can change details within
echo"<form name='details'>";
echo"<p>Surname: <input type='text'id='surname' value='".$row['Surname']."'/></p>;
<p>Telephone: <input type='text'id='phone' value='".$row['Telephone']."'/></p>;
<p>Postcode: <input type='text' id='postcode' value='".$row['Postcode']."'/></p>;
<p>House/Flat Number: <input type='text' id='number' value='".$row['Number']."'/></p>";
AJAX - sends changes to server via querystring
var sname = document.getElementById('surname').value;
var tel = document.getElementById('phone').value;
var num = document.getElementById('number').value;
var pcode = document.getElementById('postcode').value;
var queryString = "?username=" + username +"&email="+email....";
ajaxRequest.open("GET", "url" + queryString, true);
ajaxRequest.send(null);
PHP - execute update command
//connect to server
...
//get variables
$sname = $_GET['sname'];
$pcode = $_GET['pcode'];
$tel = $_GET['tel'];
$num=$_GET['num'];
//process update
$update ="UPDATE User SET Surname='$sname',Telephone='$tel',Number='$num',
Postcode='$pcode' WHERE Username='$username'";
//if query, display success
if(mysqli_query($update))
{
echo"success";
}
else
{
echo"error";
}
//else display error
The query executes fine, but the values aren't displaying within the database. My other variables (username, password etc) all update fine. All database fields are type VARCHAR(80).
EDIT: I do have the query being executed. This still results in the surname, postcode, number and telephone field not being updated.

Answer 1

Ignoring for the moment all the other issues with this code and approach (SQL injection issues, GET vs. POST issue, etc.), and dealing with the update not changing things as expected, there are a couple of things to check.
Try outputing the update query in your logs and make sure that it actually looks like what your expecting. It could be that the values you're meaning to push across the wire are not making it into the query or that.
Verify that running the query by hand in an standalone SQL client (mysql, squirrel, etc...) Actually updates a record. It's entirely possible that a valid update query may not match any records. (Say the username value you're looking for does not match one that's in the database.
Not knowing your infrastructure, I'd suggest some sanity checks: Are you actually pointing at the right database? Do you have a your update wrapped in a transaction that's rolling back? etc ...
A few other tips:
I would suggest looking at PDO, in particular how Prepared Statements work. The kind of query you're building above is someone to run off with all your data or worse. While not a panacea, prepared statements are a solid first step.
Take a look at Jquery's Ajax functions. In particular the post method. It provides a simple interface for making ajax calls without having to construct special url strings. Plus, switching to a POST will avoid your data showing up in webserver logs files.