need help: error when calculate data by group

[rayzal]

	data	total
group 0	383/4	95.75
group 1	186/2	91
group 2	86	86
group 2	100	100
group 1	197/2	98.5
group 2	(null)	0
group 2	97	97
group 2	100	100
Grand total	95.75	95.75

above table is a simplified sample of table that i design using pentaho report designer, my problem is, when i try to get the sum of group 2, sometime, the data that the function take is from another group. thus i get incorrect calculation. Can someone help me to solve this issue?

edited: the data for group 2 is retrieved from db