updating table entry from edit button - php

Question

Can anyone tell me where my problem is here, this page is linked from edit buttons I have embedded on a table of all entries. However, it is entering the current data into the fields and not updating when I enter new values? Any help appreciated.
php:
<?php
include_once("config.php");
date_default_timezone_set('Europe/London');
//getting id from url
$id = $_GET['id'];
//selecting data associated with this particular id
$EditQuery = "SELECT * FROM ACW WHERE UserID=$id";
$results = sqlsrv_query ($conn, $EditQuery);
while($row = sqlsrv_fetch_array($results, SQLSRV_FETCH_ASSOC))
{
$firstname = $row['FirstName'];
$lastname = $row['LastName'];
$location = $row['location'];
}
if(isset($_POST['update']))
{
$id = $_POST['UserID'];
$firstname = $_POST['FirstName'];
$lastname = $_POST['LastName'];
$location = $_POST['location'];
// checking empty fields
if(empty($firstname) || empty($lastname) || empty($location)) {
if(empty($firstname)) {
echo "<font color='red'>First Name field is empty.</font><br/>";
}
if(empty($lastname)) {
echo "<font color='red'>Last Name field is empty.</font><br/>";
}
if(empty($location)) {
echo "<font color='red'>Location field is empty.</font><br/>";
}
//link to the previous page
echo "<br/><a href='javascript:self.history.back();'>Go Back</a>";
}
if (preg_match("/^[0-9-]+$/",$firstname || $lastname || $location)) {
echo "<font color='red'>Numbers are not valid in these fields</font><br/>";
}
} else {
//updating the table
$UpdateQuery ="UPDATE ACW SET FirstName='$firstname', LastName='$lastname', location='$location' WHERE UserID='$id'";
echo $UpdateQuery;
//echo "<font color='green'>Data has been updated.</font><br/>";
$results = sqlsrv_query ($conn, $UpdateQuery);
}
?>
form:
<form name="form1" method="get" action="edit.php">
<table border="0">
<tr>
<td>First Name</td>
<td><input type="text" name="firstname" value="<?php echo $firstname;?>"></td>
</tr>
<tr>
<td>Last Name</td>
<td><input type="text" name="lastname" value="<?php echo $lastname;?>"></td>
</tr>
<tr>
<td>Location</td>
<td><input type="text" name="location" value="<?php echo $location;?>"></td>
</tr>
<tr>
<td><input type="hidden" name="id" value=<?php echo $_GET['id'];?>></td>
<td><input type="submit" name="update" value="Update"></td>
</tr>
</table>
</form>

Answer 1

I suggest you make 3 changes:
1.0 Give the form inputs different variable names to the one collected from the database( e.g instead of $firstname give but say $firstname_form)
2.0 Your form has method as GET but you are using POST to update
3.0 Your form action page is edit.php but the fact that you are collecting the item id via GET means that your edit button must be linked to a certain edit.php?id=$item_id Hence the action page should be edit.php?id=$id
c/o your comment: Yes. Exactly what I imagined. So, for your form action replace edit.php with edit.php?id=<?php if(isset($id)){ echo $id; } ?> You are saying that, if the id exist on this page display it as paramater.

Answer 2

I wasn't asking for your link button to be changed. It is correct. To prove that it is correct, echo the id at your edit page like this
if(isset($_GET['id'])){
$id = $_GET['id'];
echo $id;
exit();
}
You can then comment or remove the echo and exit lines after confirming that the id is passed to the edit page.
Now, on your form I was saying that the action should look like this
<form action="edit.php?id=<?php if(isset($id)){ echo $id; } ?>" method="GET" name="form1">
</form>
Adjust the variable names as I suggested earlier as well as changing input verification from POST to GET. Your database should now be updated.