Users Active in Both Months | Dataford Interview Questions

SQL: find users active in both January and February.

Asked in the Round 1 (DSA + SQL + CS fundamentals) stage. Using the provided activity records for 2025, identify users with at least one activity in each month.

Output

One row per qualifying user, with columns user_id and user_name.
Include only users active in both January and February 2025.
Order by user_id ascending.

Schema

users

Column	Type	Description
user_idPK	INT	Unique user identifier
user_name	VARCHAR(100)	Display name of the user

user_activity

Column	Type	Description
activity_idPK	INT	Unique activity identifier
user_id	INT	User associated with the activity
activity_at	TIMESTAMP	Timestamp when the activity occurred

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