Assembler Upsert Date Column

Hi. I need to get a snapshot of today's data in order to compare it with tomorrow's data once we have it. The existed dataflow uses the Replace method, so by just grabbing yesterday's numbers I won't be able to track the changes.

So I created an Assembler that would grab the historical data and append today's data each day. I have an error message: `There are duplicates in the upsert key column in one of the inputs`. Below is my setup.

Essentially, I just need to find a way how to append data each day, Magic ETL and SQL on;y has Replace method...