Rolling Average Outage Duration | Dataford Interview Questions

Your question is Rolling Average Outage Duration. Start with the requirements and the two tables on the right.

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Problem

PG&E reliability analysts need to monitor how outage duration changes over time across service areas. Write a PostgreSQL query that calculates the rolling average duration of outages for each mapped PG&E service area.

Use a 30-day inclusive window, meaning each outage includes qualifying outages from the current timestamp and the previous 29 days. Exclude outage events that do not map to a known service area.

Requirements

Join outage_events to service_areas using service_area_id.
Calculate each outage duration in hours from started_at and ended_at; preserve NULL durations when an outage has not ended.
Use a window function partitioned by service area and ordered by started_at to calculate the rolling average.
Round individual durations and rolling averages to two decimal places, and order the output by service area and start time.

Schema

outage_events

Column	Type	Description
outage_idPK	INTEGER	Unique outage event identifier
service_area_id	INTEGER	References the PG&E service area
started_at	TIMESTAMP	Outage start timestamp
ended_at	TIMESTAMP	Outage end timestamp
cause	VARCHAR(100)	Reported outage cause

service_areas

Column	Type	Description
service_area_idPK	INTEGER	Unique service area identifier
service_area	VARCHAR(100)	PG&E service area name