Simple Cohort [MySQL]

gistfile1.sql

SELECT 
  cohorts.first_action, 
  cohorts.last_action, 
  COUNT(cohorts.id) AS user_count
FROM (SELECT
        MIN(DATE(created_at - INTERVAL (DAYOFWEEK(created_at) - 1) DAY)) AS first_action,
        MAX(DATE(created_at - INTERVAL (DAYOFWEEK(created_at) - 1) DAY)) AS last_action,
        user_id AS id
      FROM daily_activity_events
      GROUP BY user_id) AS cohorts
GROUP BY
  cohorts.first_action,
  cohorts.last_action
ORDER BY
  cohorts.first_action,
  cohorts.last_action;