SQL for Department Performance | Dataford Interview Questions

Write a SQL query to analyze operational performance by department at the University of Washington, including monthly totals, average turnaround time, and a comparison to the previous month.

Use the provided tables and analyze completed requests from January through March 2025. Include departments with completed requests during the period, including months with no completed requests.

Output

One row per department and calendar month.
Columns: department_name, month, completed_requests, avg_turnaround_hours, previous_month_total, and month_over_month_change.
Sort by department name, then month ascending.

Schema

departments

Column	Type	Description
department_idPK	INT	Unique department identifier
department_name	VARCHAR(100)	University of Washington department name

request_statuses

Column	Type	Description
status_idPK	INT	Unique request status identifier
status_code	VARCHAR(30)	Operational status code

service_requests

Column	Type	Description
request_idPK	INT	Unique service request identifier
department_id	INT	Department responsible for the request
status_id	INT	Current request status
request_title	VARCHAR(150)	Short operational request description
opened_at	TIMESTAMP	Timestamp when the request was opened
closed_at	TIMESTAMP	Timestamp when the request was completed

Your question is SQL for Department Performance. Start with the requirements and the three tables in the Question tab.

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Problem