how to use datediff properly tableau

Question

basically i have the same problem with this and use this solution too https://community.tableau.com/s/question/0D54T00000C6aS6/datediff-in-lod

so i want to count time diff between transaction for each transaction and for each users, basically my problem is just like this

same with that, ON interaction id = user id in my real data, so i want to know time different between date transaction for each users.

based on that, i made this on calculation DATEDIFF('day',LOOKUP(MIN([Created At]),-1), MIN([Created At]))

and here's the results

what makes me confuse is, why the first transaction of users always have time difference, instead it must be nothing because there's no time difference if you do first transaction, so how to make it not appear?

Answer 1

Create a table calc field for First

FIRST()=0

Edit the table calc so it resets ever new user id.

Now filter for False. You can remove it from Rows, I just kept it there for demo. Your calculation will still work.