Is powerquery the place to perform advanced ETL Calculations?

Question

Ive been trying to calculate a rows cost based on a rules table using powerpivot but it has melted my mind. I really dont think powerpivot is the place to do this. The ETL Process is ideally wher this price should be calculated but as im only using excel
and flatfiles, powerquery is my etl process.
What im doing is:
I have a flatfile of orders, like below.
I have a manually created table of Stores & the same for Items.
To calculate pricings i have a few rules to follow:
-If itemID 1 is ordered, and on the same order item 2 or 3 is ordered i use the special price.
-If item 3 is ordered from store 2 i use the special price.
Otherwise standard price is used.
Powerpivot is not the place to do this. Is this more suited to powerquery?
orderid itemid storeid
1 1 1
1 2 1
1 3 1
1 1 1
2 1 2
3 4 3
3 5 3
4 1 4
4 5 4
4 4 4
itemid price specialprice
1 10 5
2 10 5
3 10 5
4 10 5
5 10 5
6 10 5
7 10 5

Answer 1

In general, it is better if you can do ETL before importing data in Power Pivot.
However, in this case the result of the Power Query ETL would be in the best case a SQL query that would push the complexity down to the data source engine, and in the worst case scenario it would request a big effort to Power Query engine working with an
in-memory copy of data. This would result in a slow process time for the table.
For this specific case, if you have a large amount of data (hundreds of thousands of rows or more), you might see better performance by creating a calculated columns in Power Pivot. I'm not saying this is always the best approach, but the rule you want to
implement might be implemented in a DAX calculated column (in the Orders table) that should perform very quickly.
=
IF (
    OR (
        Orders[StoreID] = 3,
        AND (
            Orders[OrderID] = 1,
            AND (
                CONTAINS (
                    Orders,
                    Orders[OrderID], Orders[OrderID],
                    Orders[ItemID], 2
                CONTAINS (
                    Orders,
                    Orders[OrderID], Orders[OrderID],
                    Orders[ItemID], 3
    RELATED ( Items[SpecialPrice] ),
    RELATED ( Items[Price] )
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