SQL Average Transaction Per Customer | Dataford Interview Questions

xAI's finance analytics team wants a per-customer view of transaction values. Write a PostgreSQL query that calculates the average transaction amount for transactions recorded during the past year. Assume CURRENT_DATE is 2026-08-29 when evaluating the sample output.

Requirements

Include only transactions from the last year, including transactions on the boundary date.
Return one row per customer_id, with the average rounded to two decimal places, ordered by customer ID.
Ignore NULL transaction amounts as PostgreSQL's AVG function does by default.

Schema

transactions

Column	Type	Description
transaction_idPK	INT	Unique transaction identifier
customer_id	INT	Customer associated with the transaction
amount	NUMERIC(10,2)	Transaction amount
transaction_date	DATE	Date the transaction occurred

Your question is SQL Average Transaction 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

Requirements

Include only transactions from the last year, including transactions on the boundary date.
Return one row per customer_id, with the average rounded to two decimal places, ordered by customer ID.
Ignore NULL transaction amounts as PostgreSQL's AVG function does by default.

Schema

transactions

Column	Type	Description
transaction_idPK	INT	Unique transaction identifier
customer_id	INT	Customer associated with the transaction
amount	NUMERIC(10,2)	Transaction amount
transaction_date	DATE	Date the transaction occurred

Your question is SQL Average Transaction 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.