Doug Lane (10/11/2010)
Does the query return the date range as a column, for example "1/7 to 1/13" or does it simply pass the date and have RS do the grouping? If RS is grouping by the dates at runtime, you might want to add a field to the query that groups them by week. (A date lookup table with a WeekNumberOfYear column is handy for things like this.) This way, you can have RS group by week#, which should be easier to code and less work for RS to process.
Doug is absolutely right. SSRS would do the calculation much less efficiently and much more slowly than the database could do it.