Getting around Count Distinct in a secondary data source

Tableau won't allow the aggregation count distinct or CountD() on a secondary data source. For example when we want to count the number of orders that are in a secondary data set, where each order may have multiple lines of records, we can't do it in a simple way.

There are solutions to it before LOD is available. Given LOD, this can be done a bit more easily.

Here is an example. We have a tiled map where we need to show the number of orders from each of the US states plus DC. The order data is the superstore data set included in Tableau.

The primary data set is the tiled map which has the coordinates of each states. The superstore data is the secondary data set.

In the secondary data set, let's create a calculated field One Row per Order:

This is equivalent to de-duplication of order records: AVG() will be 1 no matter how many records per order are there. That's all we need. We got the equivalent of CountD(Order) in Sum(One Row Per Order).

The example workbook is here to be downloaded for further details. In the viz, a reference is provided using CountD() from the superstore data set. We can see the numbers are the same.

There is a solution that is similar where Max(1) is used as the aggregation which is equivalent to AVG(Number of records). I don't understand why the author claimed {Fixed} won't work. {Fixed} works in the example above.