30-Day Retention Percentage | Dataford Interview Questions

Write a SQL query to calculate the percentage of users retained after 30 days.

Treat a user as retained when they have at least one activity exactly 30 days after signup. Exclude users with a NULL signup date from the calculation.

Output

Return one row with one column named retained_percentage.
Report the percentage rounded to two decimal places, from 0 to 100.

Schema

users

Column	Type	Description
user_idPK	INT	Unique user identifier
signup_date	DATE	Date the user signed up
platform	VARCHAR(20)	Primary platform used by the user

user_activity

Column	Type	Description
activity_idPK	INT	Unique activity identifier
user_id	INT	User associated with the activity
activity_date	DATE	Date the activity occurred
activity_type	VARCHAR(30)	Type of user activity

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Problem