How to merge similar files without duplicate records

I have a couple of files that I have duplicated, then additional records added to separate files.
I am cleaning digital house. I want to eliminate the duplicate files, but keep all unique records.
How can I merge the files without keeping many duplicates?

You may find this help topic of interest.

I have 2 versions of same database, with records added to each . I want to combine them into one database, preserving all records, but with no duplicates. Does that make sense?

Import the data from one database into the other. Make sure you have a backup copy of the one that is changing.

Add an extra text field to that database and do a formulafill, filling it with exportline().

Do a SortUp in that field, followed by an Unpropagate. Sorting will make duplicate records consecutive. Unpropagate will keep the first of each value, but any duplicates below it will be made blank.

Now you select all records where that field ≠ “” and remove unselected.

You can now remove the extra text field.