Database not updating through PHP, problem with MySQL query?

[Nik Kolusion]

I have a MySQL query that PHP parses successfully, and I have a problem where the query does not update the MySQL database, when it should be doing so.

I suspect this problem is caused by the way I've implemented PHP into the MySQL query, but I an not sure and wondering if anyone can see any problem with my MySQL syntaxes, etc? They look fine to me, I've gone over this piece of code thought out earlier hours of the morning and still today can't find a solution. :S

This is code I am using - query through PHP (which draws post data from HTML):

$query = "UPDATE `products` set `category` = '".$_POST['category']."' where `id` = '".$_POST['id']."'";