sun(A1)over(partition by A2 order by A3)
以A2分组，按A3排序，求出A1的累积和。
rank() over(partition by A2 order by A3)
以A2分组，按A3排序，排列号
sun(A1)over(partition by A2 )
以A2分组，求出组中成员A1的sum
sun(A1)over(order by A3)
以A3排序，求出A1的累积和
sun(A1)over()
相当于sum(A1)
例如
SELECT p.deptno,p.ename,p.sal ,p.hiredate,
SUM(p.sal) over(PARTITION BY p.deptno ORDER BY p.hiredate) ,
SUM(p.sal) over(PARTITION BY p.deptno),
SUM(p.sal) over(ORDER BY p.hiredate)
FROM emp p
deptno ename sal hiredate a1 a2 a3
20 SMITH 800.00 1980-12-17 800 10875 800
30 ALLEN 1600.00 1981-2-20 1600 9400 2400
30 WARD 1250.00 1981-2-22 2850 9400 3650
20 JONES 2975.00 1981-4-2 3775 10875 6625
30 BLAKE 2850.00 1981-5-1 5700 9400 9475
10 CLARK 2450.00 1981-6-9 2450 8750 11925
30 TURNER 1500.00 1981-9-8 7200 9400 13425
30 MARTIN 1250.00 1981-9-28 8450 9400 14675
10 KING 5000.00 1981-11-17 7450 8750 19675
30 JAMES 950.00 1981-12-3 9400 9400 23625
20 FORD 3000.00 1981-12-3 6775 10875 23625
10 MILLER 1300.00 1982-1-23 8750 8750 24925
20 SCOTT 3000.00 1987-4-19 9775 10875 27925
20 ADAMS 1100.00 1987-5-23 10875 10875 29025