[kh99]

Why do you believe that $uid_ps is not being interpreted? Maybe you should print the $query string in to your log.

The query looks right to me but I assume that your characters db table is a custom table so we can't know for sure without seeing it.

Edit: Did you try using $this->registry->db->query_write($query) ? $db probably isn't defined because that hook is called from inside a function.