Order by in analytic functions

Question

Hi All,
Please explain on how the order by clause in an analytic function vary the results ?.For eg.I get different results for SALSUM column if I order the below query by deptno/empno.
SELECT empno en,deptno dn,sal sal,SUM(sal) OVER (partition by deptno ORDER BY deptno) salsum FROM emp;
EN     DN     SAL     SALSUM
10     1     100     525
20     1     200     525
50     1     225     525
60     2     125     275
30     2     150     275
40     3     250     250
SELECT empno en,deptno dn,sal sal,SUM(sal) OVER (partition by deptno ORDER BY empno) salsum
FROM emp;
EN     DN     SAL     SALSUM
10     1     100     100
20     1     200     300
50     1     225     525
30     2     150     150
60     2     125     275
40     3     250     250

Answer 1

Hi,
SUM(sal) OVER (partition by deptno ORDER BY deptno)
In the above example. you compute sum(sal) department wise in the ascending order of the employee id
then the sum of amt dept 1 will be 525 (since it will sum up amounts acorrding to ascending order of dept no. which must be 1 since the data is partitioned by dept no. hence amt is same accross all the records i.e. 525 accross dept no 1)
and for dept 2 = 275
SUM(sal) OVER (partition by deptno ORDER BY empno)
for the second scenario ..
it will sum up the amounts partitioning by dept no. but considering the order of employee id in ascending order.
e.g for dept 1 there are 3 employess 10,20,50 arranged in ascending order
so the sumsal for emp no 10 = 100
for 10 & 20 = 100+200 = 300
& for 10 ,20, 50 = 100+200+225 = 525
Hope this calrifies..