Could anyone tell me what's wrong with this custom expression?
I want to know the average of sales for each shop ("ID Number")
Hi @Dan1
There's no Count function with column arguments:
https://github.com/metabase/metabase/issues/11558 - upvote by clicking 
on the first post
https://www.metabase.com/docs/latest/users-guide/expressions.html#list-of-all-available-functions-for-expressions
You might be able to use Sum([sales]) / Distinct([ID Number]) but I don't know you data, so perhaps it will give wrong information.