What do you create to find the number of unique items sold per shop?

To find the number of unique items sold per shop, creating a calculation view with a counter in an Aggregation node is the most appropriate approach.

Calculation views are designed for flexible modeling and allow for complex aggregations and calculations that are essential for analytical queries. Specifically, the Aggregation node is used to summarize and group data, which is critical when you want to count the distinct items sold in various shops.

In this context, using a counter within the Aggregation node facilitates the grouping of data by shop and efficiently computes the distinct count of items sold. This method aligns with the need for aggregating data to extract meaningful insights, such as unique sales metrics per location.

Other options either do not utilize the appropriate nodes for counting distinct items or are less effective in achieving the desired outcome. For instance, using a calculated column in a Star Join node or a counter in a Projection node does not adequately address the requirement for summarizing data uniquely per shop. The restricted column in an Aggregation node, while potentially useful in certain contexts, does not specifically facilitate counting unique items, leading to less straightforward results than using a counter directly in the Aggregation node.