Calculate sum between rows when time changes

[Marco Singh]

Hi,

I have a database table which looks as follows:

id Name timestamp Value1 Value2
1 Marco 20090504 16:01:01.582 0.0000000 -0.0000400
2 James 20090504 23:01:01.582 -0.0001400 0.0000000
3 Louise 20090505 00:00:00.833 -0.0001100 -0.0001400
4 Martin 20090505 01:01:01.582 -0.0000400 -0.0001100
5 Jamie 20090505 02:01:01.582 0.0001100 -0.0000400
6 Cecilie 20090505 03:01:01.582 0.0000500 0.0001100
7 Ben 20090505 15:01:01.582 0.0000000 0.0000500
8 Amanda 20090505 16:01:01.582 -0.0000800 0.0000000
9 Ida 20090505 23:01:01.582 0.0000000 -0.0000800

The timestamp column is a varchar.

I have now tried for a week to figure this out myself, and I think it is quite straighforward, but obviously not to me :-)

What I want is to calculate some stuff everytime the hour changes to 16:00:00. In this concrete example I would for instance want to calculate all the changes in column "Value1" between the 16:00:00 times. In the concrete example that would correspond to returning row 7 with two extra columns "Sum1" = sum of "Value1" from row 1 to row 7 and "Sum2" = sum of "Value2" from row 1 to row 7.

I would appreciate some help on this so much that you can't imagine!

Thanks,
Marco