SQL Window Functions Running Total | Dataford Interview Questions

Your question is SQL Window Functions Running Total. Start with the requirements and the two tables on the right.

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Problem

Quadrint analysts need a product-level revenue trend for a reporting surface such as the Mission Operations Dashboard. Write a PostgreSQL query that summarizes completed sales by product and day, then calculates each product's running revenue total.

Requirements

Include only sales with sale_status = 'completed' and matching products.
Aggregate multiple sales for the same product and date into daily_revenue.
Use a window function partitioned by product and ordered chronologically to calculate running_total.
Treat NULL sale amounts as zero for the daily aggregation, and sort the final output by product name and date.

Schema

products

Column	Type	Description
product_idPK	INTEGER	Unique product identifier
product_name	VARCHAR(120)	Quadrint product name
lifecycle_status	VARCHAR(20)	Current product lifecycle status

sales

Column	Type	Description
sale_idPK	INTEGER	Unique sale identifier
product_id	INTEGER	Product associated with the sale
sale_date	DATE	Date on which the sale occurred
amount	NUMERIC(12,2)	Revenue amount
sale_status	VARCHAR(20)	Sale processing status