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Hi all,


This is a little hard to explain:

I have a table that contains a link to a user table (user_id), and a set of values… we’ll just call this “points.”


What I would like to do is populate another field, “points_since_last”, using “points” from that row, and “points” from the previous row with that same user_id. So the formula will be t“points” from this row] - n“points” from the previous row that has the same user_id or 0 if none exists]


Row:

ID | user_id | date | points_since_last | points

I’m not sure that this can be done… mainly because there’s no way to look up a “previous” record (as far as I know); you can only look up “first” and “last”, by way of using the record creation timestamp and the MIN/MAX lookup functions.


EDIT: There is a way, but it’s a bit of a hack – you have to make a link to the previous record:


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