Rolling 7-Day Sales Average | Dataford Interview Questions

Your question is Rolling 7-Day Sales Average. Start with the requirements and the two tables on the right.

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Problem

BASF wants to monitor daily sales trends for products tracked in its commercial sales system. Write a PostgreSQL query that calculates a rolling 7-day average of completed sales for each product.

Requirements

Aggregate completed transactions into one daily sales total per product, treating missing sales days as zero.
Generate a continuous calendar between each product's first and last completed sale.
Calculate the average across the current day and previous six calendar days using a window function.
Return product name, date, daily sales, and the rolling average, ordered by product and date.

Schema

products

Column	Type	Description
product_idPK	INTEGER	Unique product identifier
product_name	VARCHAR(100)	BASF product name
business_unit	VARCHAR(100)	Product business unit

sales

Column	Type	Description
sale_idPK	INTEGER	Unique sales transaction identifier
product_id	INTEGER	References products.product_id
sale_date	DATE	Date of the transaction
sale_amount	NUMERIC(12,2)	Transaction sales value
status	VARCHAR(20)	Transaction status