Monthly Failure Rates by Component | Dataford Interview Questions

Your question is Monthly Failure Rates by Component. Start with the requirements and the two tables on the right.

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Problem

Supermicro’s hardware analytics team monitors component validation tests across server systems. Write a PostgreSQL query that calculates monthly failure rates by component and identifies the worst-performing components within each month.

Requirements

Include only completed tests with a test_status of PASS or FAILED; exclude inconclusive or missing statuses.
Calculate total completed tests, failed tests, and failure rate as failed_tests / total_tests * 100, rounded to two decimal places.
Rank components within each month from highest to lowest failure rate using a window function. Preserve equal ranks for equal rates.
Return results ordered by month, failure rate descending, and component ID.

Schema

component_catalog

Column	Type	Description
component_idPK	INT	Unique component identifier
component_name	VARCHAR(80)	Supermicro component name
component_family	VARCHAR(50)	Component category

component_test_events

Column	Type	Description
test_idPK	INT	Unique validation test identifier
component_id	INT	Tested component identifier
tested_at	TIMESTAMP	Test completion timestamp
test_status	VARCHAR(20)	Validation result status