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Retention Rate by Cohort in SQL
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Retention Rate by Cohort in SQL

MediumSQL · PostgreSQL

Problem

Given two tables (users and events), how would you calculate the retention rate for a cohort of users?

For this exercise, use users who signed up in January 2024 and evaluate retention during the signup month and the following two months. Count a user at most once per retention month, even if they have multiple events.

Output

  1. One row per month offset, from 0 through 2.
  2. Columns: month_offset, cohort_size, retained_users, and retention_rate.
  3. Sort by month_offset ascending. Return retention rate as a percentage rounded to two decimal places.

Schema

users
ColumnTypeDescription
user_idPKINTUnique user identifier
signup_dateDATEDate the user signed up
planVARCHAR(30)User subscription plan
events
ColumnTypeDescription
event_idPKINTUnique event identifier
user_idINTUser associated with the event
event_atTIMESTAMPTimestamp when the event occurred
event_nameVARCHAR(50)Name of the recorded event
Tablesusersevents
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