Unknown column 'gaby' in 'field list'

hi i am having a problem performing an insert from my php code. Here is the code i am using

	$q = "UPDATE tbl_users
		  SET username=$username, password=$password
		  WHERE user_ID = $user_ID";
	mysql_query($q, $connection) or die(mysql_error());

Code (markup):

now i am getting the error Unknown column 'gaby' in 'field list'.

I cannot understand why i get this error as far as i can see i have used the correct syntax for an update and now it is telling me that gaby doesnt exist, which in this case is the data not the field name. any help pls?

 

add single quotation marks around $username and $password

SET username='$username'

 

ok thanks solved that however the fields in my db are still not being updated, I think I need some futher help, here is the code i am using at the moment:

<?php

require_once("config.php");


// if data has been submitted save it in db and redirect to user listing
if ($_POST["submit"]) {
	$user_ID = $_POST["user_ID"];
	$username = $_POST["username"];	
	$password = $_POST["password"];

	$q = "UPDATE tbl_users
		  SET username='$username', password='$password'
		  WHERE user_ID = '$user_ID'";
	mysql_query($q, $connection) or die(mysql_error());
	//$id = mysql_insert_id($connection);
	header("Location: users.php");	

// if user_ID present in URL search for that record and display page in edit format
} else if ($_GET["user_ID"]) {
	$user_ID = $_GET["user_ID"];
	$q = "SELECT * FROM tbl_users 
		 WHERE user_ID = '$user_ID'";	
	$result = @mysql_query($q, $connection) or die(mysql_error());
	$user = mysql_fetch_array($result);
	$smarty->assign('user', $user);
	$smarty->display("users-edit.tpl");

}

?>

Code (markup):

 

You need to check your table structure. You could possibly make it dump mysql_error when it tries to insert.
One trick I use is writing the insert queries, and then try them in phpmyadmin.