If you are using a Command object you could add a column to your query with this logic and then group on it. Here is an example using SQL Server.
DECLARE @MyDate AS DATE
DECLARE @WeekNumber AS INT
DECLARE @FirstDayOfWeek AS DATE
DECLARE @LastDayOfWeek AS DATE
SET @MyDate = '01/04/2015'
SET @WeekNumber = DATEPART(WEEK, @MyDate) - 1 -- subtract one week because SQL Server considers 01/04/2015 to be Week 2
SET @FirstDayOfWeek = DATEADD(DAY, (0 + (DATEPART(dw, @MyDate) - 1 + 7) % 7) * -1, @MyDate)
SET @LastDayOfWeek = DATEADD(DAY, (-6 + (DATEPART(dw, @MyDate) - 1 + 7) % 7) * -1, @MyDate)
SELECT 'Week ' + CONVERT(VARCHAR(2), @WeekNumber) + ' (' +
CONVERT(VARCHAR(10), @FirstDayOfWeek, 101) + ' - ' +
CONVERT(VARCHAR(10), @LastDayOfWeek, 101) + ')'
If you are not using a Command object, then you are going to have to do this in Crystal formulas. I'll let you figure that out. Or maybe Abhilash Kumar will come to the rescue. 
I have given more details on the first and last day of week logic and much more in myFirst day of previous week with a twist document.
Enjoy,
Noel