Top Spending Categories Query | Dataford Interview Questions

ING wants a quarterly view of spending patterns among customers who were active during the most recent completed quarter. For this exercise, treat Q2 2025 as the reporting quarter, from 2025-04-01 inclusive through 2025-07-01 exclusive.

Write a PostgreSQL query to identify the three highest-spending transaction categories for ING users whose last_active_at falls within Q2 2025. Include only transactions occurring in the same quarter. Treat NULL transaction amounts as contributing zero, exclude transactions without a category, and calculate net spending by summing transaction amounts.

Requirements

Identify active users with a CTE or equivalent subquery.
Join active users to their Q2 2025 transactions.
Aggregate spending by category, order from highest to lowest total, and return exactly three categories.
Use a deterministic secondary sort by category name.

Schema

users

Column	Type	Description
user_idPK	INTEGER	Unique ING customer identifier
full_name	VARCHAR(100)	Customer name
last_active_at	DATE	Date of the customer's most recent activity

transactions

Column	Type	Description
transaction_idPK	INTEGER	Unique transaction identifier
user_id	INTEGER	Customer who made the transaction
transaction_date	DATE	Date of the transaction
category	VARCHAR(50)	Spending category
amount	NUMERIC(12,2)	Net transaction amount, including refunds

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