SQL Running Totals | Dataford Interview Questions

Your question is SQL Running Totals. Start with the requirements and the two tables on the right.

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Problem

Pratt & Whitney analysts need to monitor completed inspection effort across engine programs. Write a PostgreSQL query that summarizes inspection hours by engine model and calendar month, then calculates a chronological running total for each model.

Requirements

Join work orders to engine programs and include only work orders with status = 'Completed' and a non-null completion date.
Aggregate inspection hours by engine model and completion month, treating null hours as zero.
Use a window function to calculate the cumulative hours for each engine model, ordered by month. Return results ordered by engine model and month.

Schema

engine_programs

Column	Type	Description
program_idPK	INT	Unique engine program identifier
engine_model	VARCHAR(40)	Pratt & Whitney engine model name
aircraft_platform	VARCHAR(60)	Primary aircraft platform using the engine

work_orders

Column	Type	Description
work_order_idPK	INT	Unique work order identifier
program_id	INT	Engine program identifier from the operational work-order feed
completed_at	DATE	Date the work order was completed
status	VARCHAR(20)	Current work order status
inspection_hours	NUMERIC(8,2)	Hours recorded for the inspection