Oracle кумулативен брой с помощта на SYS_CONNECT_BY_PATH

Единствено с проба и грешка върху вашите примерни данни от SQL Fiddle, това е заявката, която връща очакваните ви данни:

SELECT SYS_CONNECT_BY_PATH(firmware_version, '/') path_,
  firmware_version,
  device_count,
  dmc_id,
  charging_group_id,
  IMAGE_PREREQUISITE,
  (SELECT SUM(device_count)
  FROM DM_TEMP_SUMMING_DVC_BY_FW t2
  START WITH t1.firmware_version = t2.firmware_version
        and T1.dmc_id = T2.dmc_id
        and T1.charging_group_id = T2.charging_group_id
  CONNECT BY nocycle PRIOR firmware_version=image_prerequisite and prior dmc_id = dmc_id and prior charging_group_id = charging_group_id
  ) sum_device
FROM DM_TEMP_SUMMING_DVC_BY_FW t1
START WITH image_prerequisite IS NULL
CONNECT BY nocycle PRIOR firmware_version = image_prerequisite
    and prior dmc_id = dmc_id
    and prior charging_group_id = charging_group_id

Забележка: Да, charging_group_id и dmc_id са много важни за вашия очакван резултат, както krokodilko правилно спомена в горния си коментар.