Append several Sharepoint files with different header names

Hi,

I have 3 files that live on Sharepoint. Each week another one is added. They have a few columns in common, but also all have one or more different header names, that don't exist in the other files. I would like to pick up the files and then append them. If there is a column name that does not exist in the other files, that is fine, it can have null values.

Basically the question is like this:

Help would be much appreciated!