If I understand you correctly it isn't that hard to do.
You need to do a full outer join between staging and the history and filter the records where you have a join to the staging.
Then you need to read the date from the staging again and join this to the remaining history records.
This join can be an inner join if you create a dummy join port in both streams with value = 1.
Hope this helps
Was your problem solved or did I misunderstand the issue?
So apparently i was able to identify the records that exist in stage but not in history. Got the key from history and file date from stage and able to update the table. So i have SQ->exp tx-> update strategy-> target.
Thank you for all your help.