Update existing nodes with fields from XML or CSV There are 2 greate modules for importing nodes Feeds and Feed Import. Is there a way to update fields of existing nodes on import from XML or CSV file?

For example, there is an XML feed from another website with products (id + price) and file with additional data for the same products (id + description). How to import both sources into the same node in Drupal?
You need to set up feeds and feeds_xpathparser. You could found a good start for configuring all this here : http://www.drupalprogrammer.co.uk/2012/12/use-feeds-module-to-import-xml-data-in.html

Concerning your concern about updating, you can do this by configuring the guid as your external unique id. In the screenshot provided, you can see in my case the xml tag used for unique id is simply &lt;id&gt;.



Then, you just have to configure the node processor so that it will "Update existing node" when it found a duplicate as shown on the screenshot below.