Sales and Transactions Per Customer | Dataford Interview Questions

A sales analytics team needs a report of customer activity during a fixed 30-day reporting period. Write a SQL query to calculate each customer's total sales volume and transaction count for transactions from August 16, 2026 through September 15, 2026, inclusive.

Output

One row per customer with at least one transaction in the reporting period.
Return customer_id, total_sales_volume, and transaction_count.
Include transactions whose amount is NULL in the transaction count, but treat NULL amounts as contributing zero to total sales volume.
Sort by customer_id in ascending order.

Schema

customer_transactions

Column	Type	Description
transaction_idPK	INT	Unique transaction identifier
customer_id	INT	Identifier of the customer who made the transaction
transaction_at	TIMESTAMP	Timestamp when the transaction occurred
amount	NUMERIC(12,2)	Sales amount for the transaction

Your question is Sales and Transactions Per Customer. Start with the requirements and the one table in the Question tab.

Run and submit as often as you like. When you're ready, talk me through your approach or go straight to the code.

Problem

Output

One row per customer with at least one transaction in the reporting period.
Return customer_id, total_sales_volume, and transaction_count.
Include transactions whose amount is NULL in the transaction count, but treat NULL amounts as contributing zero to total sales volume.
Sort by customer_id in ascending order.

Schema

customer_transactions

Column	Type	Description
transaction_idPK	INT	Unique transaction identifier
customer_id	INT	Identifier of the customer who made the transaction
transaction_at	TIMESTAMP	Timestamp when the transaction occurred
amount	NUMERIC(12,2)	Sales amount for the transaction

Your question is Sales and Transactions Per Customer. Start with the requirements and the one table in the Question tab.

Run and submit as often as you like. When you're ready, talk me through your approach or go straight to the code.