30-Day Retention by Channel | Dataford Interview Questions

NovaPlay wants to measure how well each acquisition channel retains new users after signup. Write a PostgreSQL query to calculate 30-day retention by acquisition channel.

A user is considered retained if they have at least one activity event on or after signup_date + 30 days and on or before signup_date + 60 days. Use each user's acquisition channel from the acquisitions table.

Requirements

Return one row per acquisition channel.
For each channel, calculate:
- total signed-up users
- retained users
- 30-day retention rate as a percentage rounded to 2 decimals
Include users even if they have no matching acquisition row; label those as 'Unknown'.
Order results by retention rate descending, then channel name ascending.

Schema

users

Column	Type	Description
user_idPK	INT	Unique user identifier
signup_date	DATE	Date the user signed up
country	VARCHAR(50)	User country

acquisitions

Column	Type	Description
acquisition_idPK	INT	Unique acquisition record identifier
user_id	INT	User tied to the acquisition record
channel	VARCHAR(50)	Acquisition channel
campaign_name	VARCHAR(100)	Marketing campaign name

activity_events

Column	Type	Description
event_idPK	INT	Unique activity event identifier
user_id	INT	User who generated the event
event_date	DATE	Date of the activity event
event_type	VARCHAR(50)	Type of user activity

Your question is 30-Day Retention by Channel. Start with the requirements and the three tables in the Question tab.

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