Oracle按日期累计求和

SELECT DISTINCT HIRE_YEAR_MONTH, DEPARTMENT_ID,  COUNT_
FROM (
SELECT
DEPARTMENT_ID,
TO_CHAR(HIRE_DATE, 'yyyy/mm') HIRE_YEAR_MONTH,
COUNT(*) OVER(PARTITION BY DEPARTMENT_ID ORDER BY TO_CHAR(HIRE_DATE, 'yyyy/mm'))
AS COUNT_
FROM HR.EMPLOYEES)
ORDER BY DEPARTMENT_ID, HIRE_YEAR_MONTH;

SELECT DEPARTMENT_ID,
TO_CHAR(HIRE_DATE, 'yyyy/mm') HIRE_YEAR_MONTH,
COUNT(*),
SUM(COUNT(*)) OVER(PARTITION BY DEPARTMENT_ID ORDER BY TO_CHAR(HIRE_DATE, 'yyyy/mm')) AS COUNT_
FROM HR.EMPLOYEES
GROUP BY DEPARTMENT_ID, TO_CHAR(HIRE_DATE, 'yyyy/mm')