How to crate formula in crystal report in group by section?

[nur alam]

I have a table named sub_detailsN. table structure is:

CREATE TABLE [dbo].[sub_detailsN](
[SQuarter] [varchar](6) NULL,
[months] [varchar](4) NULL,
[mem_sl] [int] NOT NULL,
[amount] [float] NULL,
[salesId] [varchar](10) NULL,
[sdate] [date] NULL,
[Rate_interest] [float] NULL,
[lastPayDate] [date] NULL,
[interest] [float] NULL,
[DMonth_interest] [float] NULL,
[status] [varchar](1) NULL
)

I add this table to crystal report and used
ReportDocument objRpt = new rptSubscription Dtls();
if ((cmbMember.Tex t != "")&& (cmbRef.Text !=""))
{
objRpt.RecordSe lectionFormula = "{sub_detailsN. mem_sl}=" + cmbMember.Selec tedValue + " and { sub_detailsN.SQ uarter}='" + cmbRef.Selected Value + "' ";}
else if (cmbMember.Text != "")
{
objRpt.RecordSe lectionFormula = "{sub_detailsN. mem_sl}=" + cmbMember.Selec tedValue + "";
}
else if (cmbRef.Text != "")
{
objRpt.RecordSe lectionFormula = "{sub_detailsN. SQuarter}=" + cmbRef.Selected Value + "";



I have used a formula

if Sum ({sub_detailsN. DMonth_interest })>3 then 'Last and Final Reminder' else 'Bill'
}
And place it in a group based on mem_sl

It always return maximum value of the entire table
But I need maximum value based on each mem_sl

How can I do it?