WITH usrs AS
  (SELECT *
   FROM
     (SELECT user_id
      FROM tools_shop.orders) AS o
   LEFT JOIN
     (SELECT user_id
      FROM tools_shop.users) AS u ON o.user_id = u.user_id
   LEFT JOIN tools_shop.events AS e ON e.user_id = o.user_id),
     ord AS
  (SELECT CAST(DATE_TRUNC('month', event_time) AS date) AS mnth,
          COUNT(event_name) AS cnt
   FROM usrs
   GROUP BY CAST(DATE_TRUNC('month', event_time) AS date))
SELECT *,
       sum(cnt) OVER (
                      ORDER BY mnth)
FROM ord