Get Running total in Db2

Using an aggregate function in SQL is pretty straightforward. However we sometimes need to have other columns in a table along with the corresponding aggregate we are trying to calculate. This is not possible if we use the functions in the traditional way using group by clause. 

Lets take an example. Below is the table BookSales. 

BookID	DateOfSale	SaleCnt
1001	2016-01-01	33
1001	2016-01-02	10
1001	2016-01-03	16
1002	2016-01-04	22
1001	2016-01-05	12
1001	2016-01-06	20
1002	2016-01-07	10
1001	2016-01-08	23
1002	2016-01-09	12
1002	2016-01-10	50
1001	2016-01-12	14
1001	2016-01-13	24

What I want to find is the running total for each book along with the dates. The result I am expecting is something like this

BookID	DateOfSale	SaleCnt	RunningTot
1001	2016-01-01	33	33
1001	2016-01-02	10	43
1001	2016-01-03	16	59
1001	2016-01-05	12	71
1001	2016-01-06	20	91
1001	2016-01-08	23	114
1001	2016-01-12	14	128
1001	2016-01-13	24	152
1002	2016-01-04	22	22
1002	2016-01-07	10	32
1002	2016-01-09	12	44
1002	2016-01-10	50	94

Query

SELECT A*,

       SUM(SALECNT) OVER(PARTITION BY BOOKID

                         ORDER BY DATEOFSALE) AS RUNNINGTOT

FROM BOOKSALES A;

You could have the same result even if we change the display order using OrderBy clause in the query.

For Example

SELECT A*,

       SUM(SALECNT) OVER(PARTITION BY BOOKID

                         ORDER BY DATEOFSALE) AS RUNNINGTOT

FROM BOOKSALES A

ORDER BY BOOKID, DATEOFSALE DESC;

---------------------------- RESULTS IN ------------------------------

BookID	DateOfSale	SaleCnt	RunningTot
1001	2016-01-13	24	152
1001	2016-01-12	14	128
1001	2016-01-08	23	114
1001	2016-01-06	20	91
1001	2016-01-05	12	71
1001	2016-01-03	16	59
1001	2016-01-02	10	43
1001	2016-01-01	33	33
1002	2016-01-10	50	94
1002	2016-01-09	12	44
1002	2016-01-07	10	32
1002	2016-01-04	22	22