SQL Joins and DNS Working | Dataford Interview Questions

Tell me about a time you debugged DNS-related issues and fixed SQL join queries to get correct results.

For the supplied records, write a PostgreSQL query that returns resolved DNS debugging records with at least one verified SQL join fix. Match fixes to their corresponding debugging record and exclude unverified fixes.

Output

One row per qualifying debugging record, with incident_id, hostname, resolved_at, verified_join_fixes, and latest_fix_at
Include only resolved records having at least one verified fix
Order by latest_fix_at descending, then incident_id ascending

Schema

dns_incidents

Column	Type	Description
incident_idPK	INT	Unique debugging incident identifier
hostname	VARCHAR(255)	Hostname involved in the DNS issue
resolution_status	VARCHAR(30)	Current resolution state
resolved_at	TIMESTAMP	Time the incident was resolved

sql_join_fixes

Column	Type	Description
fix_idPK	INT	Unique SQL fix identifier
incident_id	INT	Incident associated with the fix
join_type	VARCHAR(30)	Join type involved in the corrected query
validation_status	VARCHAR(30)	Validation state of the SQL fix
fixed_at	TIMESTAMP	Time the fix was recorded

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Problem