Hi there,
In Column Expressions node you can also specify column by its index. So column(0) is addressing first column in your table. If you have a fix number of columns you can use that trick.
To use Column Comparator in a loop you can try something like this:
And here is workflow on KNIME Hub. It works if tables have same structures. Take a look and if any questions feel free to ask.
Br,
Ivan