SQL Sales Metrics With Edge Cases | Dataford Interview Questions

Your question is SQL Sales Metrics With Edge Cases. Start with the requirements and the two tables on the right.

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Problem

Netflix wants a monthly sales view covering every retail store, including months in which a store had no sales. Write a PostgreSQL query for January through March 2025.

Requirements

Return one row for every store and every month in the reporting period.
Calculate transaction count, total sales, and average sale amount.
Represent missing sales as zero for count, revenue, and average sale amount.
Preserve stores with no matching sales and exclude sales outside the reporting period.

Schema

stores

Column	Type	Description
store_idPK	INT	Unique store identifier
store_name	VARCHAR(100)	Name of the store
region	VARCHAR(50)	Geographic region containing the store

sales

Column	Type	Description
sale_idPK	INT	Unique sale identifier
store_id	INT	Store associated with the sale
sale_date	DATE	Date on which the sale occurred
amount	NUMERIC(10,2)	Sale amount
sale_channel	VARCHAR(30)	Channel used for the sale