How to update an output file, if there is a new record in the original file

[maheshkumar7]

I have a file with some information, it also has a unique identified for each row. Is it possible that the output file only adds row below with new records and not update the whole file? The reason is that in that output file someone will be adding some notes in another column and I want that to remain as it is. If there are new records then it can just add rows below, and not change those notes in the extra column? Any ideas are appreciated. 

I did try to use Append but not able to work it out for some reason.

Thanks,

[pzlatunic]

On the output tool, are you able to change the output options to Append to Existing Sheet?

[maheshkumar7]

I get that but when I use that option it just duplicates the old ones too... E.g. if there are 10 rows it will show 20 rows (duplicate) in case there is no new record in original file. 

[pzlatunic]

Oh I see. Could you union the existing file with the result of your workflow and have that unioned result be the new output? In this case you would need the output options set to Overwrite File (Remove). 

[maheshkumar7]

I tried that, but it just duplicates it. Record1 should only exist once, but since I ran it twice so there are three duplicates now.  Each record has a unique identifier too maybe I can use that some how?

[maheshkumar7 · Accepted solution]

UPDATE: I managed to do this by using the Join tool. On the Left I input the existing file, and on the right i input output from the file which has updated information (or not). On the output of Join tool I add a filter on the right and use the formula IsNull([Unique identifier]) and then output the file and use the append option. So if there are no new records, it does not update, and if there are, then a new row is added.