Many data warehouses include calendar tables to handle special situations like fiscal calendars, company holidays, shift rotations, and other scenarios. Tables like this simplify the process of excluding things like non-working days from DATEDIFF() calculations, to name only one example.
I would like to see this functionality inside of Tableau. I envision it working similar to custom geocoding where a user defines a custom calendar then attaches it to Tableau using a .csv file. There may be a true/false flag for "workday" (or other custom fields) which could be referenced in a calculation. For example, if I want to count the calendar days between two dates, I can use DATEDIFF("day", [Start],[End]). With a custom calendar table defining a field called "workday" I could also count up only the working days between those dates like this: DATEDIFF("workday", [Start],[End]).
The below ideas would all be addressed by a solution like this. I have used calendar tables in databases and found them highly valuable. As we know, not every database has one and not every Tableau user can easily add one to the underlying database. Therefore, some ability to include it in workbooks as a custom calendar definition would be useful.
This method would also simplify the calculations for handling date issues listed extensively here: