Joiner - how to fill only one row of a category?

Hey,

first time poster here … and I like to thank all of you who have posted and answered here - I learned a lot!

But now I am running into a problem that I cannot solve by myself. I am preparing a data set for consumption in a Process Mining tool and have calculated the activity cost for each activity (row) in the data set. Then I used the Group By node to calculate the overall cost for the case (column Case ID).

So far, so good. However, when I join the case cost with the original data set, the Joiner node fills the case cost into every row with that case ID. That leads to a multiple of the overall case cost in the Process Mining tool.

What I want is that it only fills the first record for each case - the green checkbox in the screenshot in the lower right corner. All other cells in that column for that case should be empty (the orange highlight).

How can that be accomplished in Knime?

Thanks in advance,

Roland