Columns selector missing

Is there something that would cause the column selector in the notebook editor to be hidden on the first table?
On a new question, selector is visible:

However I'm trying to edit an existing question and the selector isn't there:

I'm on v0.39.4

Hi @Bungle
You are not showing the full context. You are likely summarizing the question, which means the columns doesn't really mean anything, since your result will be the metrics and groupings you define.

You're correct, I am summarizing. So in order to add columns, I need to first remove the summarization?

@Bungle Think of it in terms of SQL - let's say you have a Count metric, then your SQL would be:
select count(*) from table
What's the point of being able to select any of the columns?

Right, but let's say you'd want a summary by some other column. E.g. total sales by customer. In SQL you'd do
select customer, sum(sales) from table group by customer
So you would be selecting the column at the beginning. I was expecting to do the same in the notebook editor. But I think I understand now, it seems everything is handled in the Summarize section: