last interaction date

Can you talk about the usecase a bit? What do you mean by an "interaction" in this context?

I am adding my data to another database and require a 'last transaction date' for each user.  This would be the most recent interaction the person had with one of our marketing campaigns.  Could be actions like clicking through an email, registering or attending an event, or filling out a form. 

Unfortunately 'updated date' won't work because that could have been triggered by an internal event and not necessarily the individual in question taking action.  Ideally, I would like to set up some campaign where if 'clicked email' is true, then it would populate the transaction field with the date of their most recently clicked link, and so on. 

I would probably also need to know how to sort through which of the actions is the most recent. For example, if one person had clicked email and attended event, I would want to be able to evaluate the date for both of the fields that I have created and then determine which is the most recent and populate that into a fourth field.

Any suggestions would be apprciated, maybe I can approach it a different way.  Ultimately, I need to be able to take the date information of an activity and populate it into a field.

Well, are you syncing that underlying data using the API? Wouldn't you be able to infer that date yourself?

I'm just trying to figure out how that data gets used. It might also be possible to run a batch campaign every night which writes the current date into a field if a relevant interaction happened on that day.

I am not sure how to populate a field with the data.  I can look at individiuals and determine the last transaction data based on their activity log, but cannot do so for 29,000 people. 

Is there any way to run a campaing that would take the date from one field and populate it into another field? 

Doing it historically is going to be tricky- I don't know of a good way.

If you wanted to do it going forward, I'd create a nightly recurring batch campaign which looked for leads which had that activity in the last day and then set the value on the last date field to the current date.