I have a problem where i want to set a base date to a date time variable in the database. I would then use the base date for my aggregations. And the days subsequent to this base date would be categorised as Day1, Day2 and so on.
So for example, if I want to see cohorts of orders created by the base date - I would want the calculated after this date. I don't want to do this using a date filter.
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It seems like you could use the DATE function to convert your field, like this:
DATE([Acquisition Date])
If you don't already have the year value stored, but have a method in mind to add it, you could use MONTH([Acquisition Date]) to obtain the month and date and DAY([Acquisition Date]) to obtain the date. You could then use MAKEDATE function to build the date or MAKEDATETIME function to build the datetime value.
Once it's stored as a date value, you could use DATEADD to add and subtract days to it as needed.
There are multiple formulas available for converting Tableau dates, described here: https://help.tableau.com/current/pro/desktop/en-us/functions_functions_date.htm
Is this what you're looking for?