Compare Signup Cohorts by Retention | Dataford Interview Questions

Your question is Compare Signup Cohorts by Retention. Start with the requirements and the two tables on the right.

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Problem

StreamWave wants to compare how different signup cohorts behave after registration. Write a SQL query to measure 30-day engagement by monthly signup cohort.

Requirements

Define each user's cohort as the month of their signup_date.
For each cohort month, calculate:
- total users in the cohort
- users with at least one session_start event within 30 days of signup
- the percentage of engaged users in the cohort
Return one row per cohort month.
Order results by cohort month ascending.

Schema

users

Column	Type	Description
user_idPK	INT	Unique user identifier
signup_date	DATE	Date the user signed up
acquisition_channel	VARCHAR(50)	Marketing channel that acquired the user

events

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