Can this question be modelled as a metabase query?

What percentage of orders in April 2020 were from new customers?

A new customer is keyed on email address.

Order table

OrderId : guid
CustomerEmail : string
ProductOrdered : string
OrderedAt : datetime

The way I would approach in SQL (or think I would) would be a a query CTE orders_before_april2020 grouped by email, and a redundant count field.
Then produce another CTE of orders in april that has email, order_before_april_2020_count based on an left outer join to the CTE, then aggregate by by count.

Then group_by to give on a condition of order_before_april_2020_count > 0

Then an MB pie chart.

This currently isn’t possible right for a analyst to do with just the Order table data source in MB?

After a million combinations of various joins, I think the answer is no. It’s an extremely common question but the absence of coalecation and group by expression makes it a no starter.

I think you can get someway there by adding a virtual field to your data source of customer_email_last_ordered_before_this_order nullable(datetime) but still don’t think you can get to a pie chart… Ah but then that field would be wrong if customer ordered twice in april