SQL Top Customers Per Month | Dataford Interview Questions

Your question is SQL Top Customers Per Month. Start with the requirements and the two tables on the right.

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Problem

Airtel Payments Bank wants a monthly view of its highest-value customers. Write a PostgreSQL query to find the top three customers by total successful transaction amount in each calendar month.

Requirements

Include only transactions with status = 'SUCCESS' and a positive, non-null amount.
Join transactions to customers to return the customer's name.
Aggregate transaction amounts by month and customer, rank customers within each month, and return exactly the top three per month.
Display the month as YYYY-MM and order the results by month and rank.

Schema

customers

Column	Type	Description
customer_idPK	INTEGER	Unique customer identifier
customer_name	VARCHAR(100)	Customer's full name

transactions

Column	Type	Description
transaction_idPK	BIGINT	Unique transaction identifier
customer_id	INTEGER	Customer who initiated the transaction
transaction_timestamp	TIMESTAMP	Transaction date and time
amount	NUMERIC(12,2)	Transaction amount in Indian rupees
status	VARCHAR(20)	Transaction processing status