7-Day Rolling Average Transactions | Dataford Interview Questions

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

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Problem

Chase fraud and customer analytics teams need a daily activity baseline for customers using Chase Checking. Write a PostgreSQL query that calculates each customer's 7-day rolling average of posted Checking transactions.

Requirements

Join customers to transactions and include only active Chase customers with account_type = 'CHECKING'.
Treat a NULL transaction status as POSTED, exclude explicitly reversed transactions, and aggregate transactions by customer and calendar date.
Fill dates with no transactions as zero-count days between each customer's first and last qualifying transaction.
Use a window function to calculate the average of the current date and up to the six preceding calendar dates.
Return customer_id, customer_name, transaction_date, daily_transaction_count, and rolling_avg_7d, rounded to two decimals. Order by customer and date.

Schema

customers

Column	Type	Description
customer_idPK	INT	Unique Chase customer identifier
customer_name	VARCHAR(100)	Customer display name
is_active	BOOLEAN	Whether the customer is currently active

transactions

Column	Type	Description
transaction_idPK	INT	Unique transaction identifier
customer_id	INT	Customer associated with the transaction
transaction_date	DATE	Date on which the transaction posted
account_type	VARCHAR(30)	Account category for the transaction
status	VARCHAR(30)	Transaction processing status