Grouping by the first two characters of ItemClass fails in Acumatica Report Designer

The issue has been resolved!I joined the INItemClass table and modified the group statement to =Left(Trim([INItemClass.ItemClassCD]), 2).I suspect there was an unknown problem with the system's automatic conversion of InventoryItem.ItemClassID. It’s labeled as an ID, but it actually displays the CD value on the screen, which is probably where the error occurred.

​@ray20  I think it’s not really a problem, so much of a “how it works”. 

But I agree it’s confusing to learn how it works in the first place and could probably use more documentation.

Theory:

When you add a formula to the data field like that you’re interacting with the underlying called field (the ID)

The UI has smarts to say “I should display the CD instead of the ID”, but that’s processed as a layer on top of anything done in the actual data handling.

If you’re trying to manipulate data from a CD value, I’d always recommend joining the referred table explicitly and acting on it there, the other issue is just that any calculation that relies on the in built ID conversion slows the database calls down due to the way BQL queries things. (Since the joins don’t get optimized properly).  

It’s the same underlying reason you get warnings displayed in the Generic Designer if you try to use derived CD values like that in where clauses. (Which sometimes are referred to as ID, because the UII is trying to be clever for you)