Crystal Report 8.0, Summary function !

Friends,

I'm working with crystal report 8.0 and SQL server.

I need to create a formula in group section, which should return the summary value of next group.

Or is there any function for get summary value if the group value is 'x'. same as SumIF( , , ) in excel.You need to write a formula having the code

If groupvalue='x' then
{field}

and use the summary using this