SQL Running Totals | Dataford Interview Questions

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

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