If the intent is to use a parameter to limit the rows, the intent and solutions here are not optimal.
Since the data is stored as a string, create a date range parameter, and then convert the date parameter to a string and use that in the record selection formula, otherwise all processing will be done in Crystal, which can be punishingly slow.
So for the record selection formula, try:
{table.datesring} >= totext(minimum({?Daterangeparm}),"yyyyMMdd"

and
{table.datesring} <= totext(maximum({?Daterangeparm}),"yyyyMMdd"
Always check the Database->Show SQL Query to determine if it's being passed to the database.
If it's not a date range parm, eliminate the minimum().
-k