Runsum in Query by group

[ehe]

Hi,
I am trying to do a running sum in a query by account. Here is what i need the output to look like:

TRANID Account DateTime Amount RunSumAmount
1 1 1-jan-09 100 100
2 1 2-jan-09 250 350
3 1 3-jan-09 50 400
4 2 1-jan-09 60 60
5 2 2-jan-09 70 130

I saw this answer which is very simple but it does not address the diffierent accounts.
https://www.pcreview.co.uk/forums/thread-1184294.php

thank you