SQL Set Difference for Actions | Dataford Interview Questions

Virtusa's client engagement portal records user actions separately from its audit service. Identify users who performed a case_submitted action in the portal during January 2025 but have no matching case_submitted record in the audit table during the same period.

Write a PostgreSQL query that returns each qualifying user once.

Requirements

Include only case_submitted actions occurring from 2025-01-01 through 2025-01-31.
Use an anti-join pattern to exclude users with a matching audit action.
Return the user ID and name, ordered by user ID ascending.
Do not treat other action types, actions outside January, or audit records for different users as matches.

Schema

users

Column	Type	Description
user_idPK	INT	Unique user identifier
full_name	VARCHAR(100)	User's full name

portal_actions

Column	Type	Description
action_idPK	INT	Unique portal action identifier
user_id	INT	User who performed the portal action
action_name	VARCHAR(50)	Name of the portal action
action_at	TIMESTAMP	Timestamp when the portal action occurred

audit_actions

Column	Type	Description
audit_idPK	INT	Unique audit record identifier
user_id	INT	User associated with the audit action
action_name	VARCHAR(50)	Name of the audited action
action_at	TIMESTAMP	Timestamp when the audit action occurred

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