SQL for Bank Customer Expenses | Dataford Interview Questions

Your question is SQL for Bank Customer Expenses. Start with the requirements and the two tables on the right.

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Problem

Business Context

Fidelity Full View aggregates a customer's financial activity across connected accounts. A reporting team needs to identify each customer's peak monthly spending period.

Task

Write a PostgreSQL query that groups monthly expense records by Fidelity Full View customer and returns the month with the highest combined expense across all expense columns.

Requirements

Treat NULL expense values as zero when calculating the monthly total.
Calculate the largest individual expense category for the selected peak month using the expense columns.
Return every customer, including customers with no expense records.
If a customer has tied peak months, select the later month.

Schema

customers

Column	Type	Description
customer_idPK	INT	Fidelity customer identifier
customer_name	VARCHAR(100)	Customer display name

monthly_expenses

Column	Type	Description
expense_idPK	INT	Unique monthly expense record identifier
customer_id	INT	Customer associated with the expense record
expense_month	DATE	First day of the expense month
housing_expense	NUMERIC(12,2)	Monthly housing expense
groceries_expense	NUMERIC(12,2)	Monthly grocery expense
utilities_expense	NUMERIC(12,2)	Monthly utility expense
transport_expense	NUMERIC(12,2)	Monthly transportation expense