Comprehensive Detailed Explanation
We need to calculate the proportion of the total quantity of each sales order represented by each product within the sales order.
Step 1: Analyze the requirement
Table: SalesOrderDetail
Columns: OrderQty, ProductID, SalesOrderID
Each row = one product in a sales order.
Requirement: For each SalesOrderID, calculate what percentage each product contributes to the total order quantity.
This means we must:
Calculate the total order quantity per SalesOrderID.
Divide each product's OrderQty by that total.
Express it as a percentage.
Step 2: Evaluate the options
A). Uses OVER(ORDER BY ProductID)
Wrong: ORDER BY does not segment data, it only defines sequence. We need grouping by sales order.
B). Uses OVER(PARTITION BY ProductID)
Wrong: This would calculate percentages per product across all sales orders, not per sales order.
C). Uses OVER(PARTITION BY SalesOrderID)
Correct: This computes the total OrderQty per SalesOrderID and divides each product's quantity by that total.
Exactly what the requirement asks.
D). Uses OVER(ORDER BY SalesOrderID)
Wrong: Again, ORDER BY just sequences rows, does not group them.
Step 3: Correct Query
SELECT
SalesOrderID,
ProductID,
OrderQty,
CAST(1. * OrderQty / SUM(OrderQty)
OVER(PARTITION BY SalesOrderID) * 100 AS DECIMAL(5,2))
AS PercentByProductID
FROM Sales.SalesOrderDetail;
Why Option C is Correct
PARTITION BY SalesOrderID ensures the denominator is the total quantity for the current order.
This produces the correct percentage breakdown of each product inside its sales order.
References
T-SQL Window Functions
Aggregate Functions with PARTITION BY
Microsoft Fabric Warehouse T-SQL Support