Cumulative Comments by User | Dataford Interview Questions

Find the cumulative number of comments written by each user over time, handling edge cases where users have days with zero activity.

Use the users and comments tables. Consider the full date range present in comments, and include every user on every date in that range, including users with no comments.

Output

One row per user and calendar date, with user_id, username, activity_date, daily_comments, and cumulative_comments.
Include zero-activity days and users with no comments.
Order by user_id, then activity_date ascending.

Schema

users

Column	Type	Description
user_idPK	INT	Unique Reddit user identifier
username	VARCHAR(50)	Reddit username

comments

Column	Type	Description
comment_idPK	INT	Unique comment identifier
user_id	INT	User who authored the comment
comment_date	DATE	Calendar date when the comment was written
body	TEXT	Comment text

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