Using Moving Window Functions | Dataford Interview Questions

How do you use moving window functions in SQL?

Write a PostgreSQL query that calculates each seller's daily completed order amount and its three-row moving average. The moving window includes the current date and up to the two preceding seller dates. Use the provided tables and include only sellers with completed orders.

Output

One row per seller and order date
Columns: seller_id, seller_name, order_date, daily_amount, moving_average
Sort by seller_id, then order_date ascending

Schema

sellers

Column	Type	Description
seller_idPK	INT	Unique seller identifier
seller_name	VARCHAR(100)	Seller display name

orders

Column	Type	Description
order_idPK	INT	Unique order identifier
seller_id	INT	Seller associated with the order
order_date	DATE	Date the order was placed
order_amount	NUMERIC(10,2)	Order amount
status	VARCHAR(20)	Order processing status

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