Comprehensive and Detailed Explanation From Exact Extract:

In Workday Prism Analytics, calculating the total purchase amount for each customer requires aggregating data by customer ID. According to the official Workday Prism Analytics study path documents, the appropriate transformation stage for this task is a Group By stage (option C). The Group By stage allows you to group the dataset by a specific field (e.g., customer ID) and apply aggregation functions, such as SUM, to calculate the total purchase amount for each customer. For example, you would group by customer ID and use SUM(purchase_amount) to compute the total. This stage reduces the dataset to one row per customer, with the aggregated total purchase amount, enabling the desired analysis over the entire period.

The other options are incorrect:

A. Join: A Join stage combines data from two datasets based on a matching condition, but it does not aggregate data to calculate totals.

B. Union: A Union stage appends rows from one dataset to another, which does not help with calculating totals per customer.

D. Explode: An Explode stage transforms multi-instance fields into multiple rows, which is unrelated to aggregating purchase amounts.

The Group By stage is the correct choice to aggregate purchase amounts by customer, facilitating the analysis of totals over the entire period.