But when I try to add this to the above table, I get:
This doentn't make much sense to be. What does it mean that "the date column is not unique" - does it expect unique date values? In the context of my example, this is nonsense as there are many orders on some days and none on many other days!
I'm now trying to set up a Dates table, but am getting weird results at the first step - as you wan see from the amage below, I'm aiming to set up a dates table for all days between 2010 and 2035 but Power BI in starting my table on 23/6/1906(!) and ending it on 16/016/1937 (!!)