SELECT
  count(DISTINCT u.userID)

FROM
  `uptimerobot-001.ur.users` u
  LEFT JOIN
    `uptimerobot-001.ur.monitors` m

  ON
   u.userID = m.userID

WHERE
  userRegisterDateTime BETWEEN '2022-09-01 00:00:01' AND '2022-09-31 23:59:59'
  AND monitorCreateDateTime BETWEEN '2022-09-01 00:00:01' AND '2022-09-31 23:59:59'
  AND monitorID IS NOT NULL