How to manage the substitution variable / parameter in crystal

Question

I have developed a Crystal report in BO XI. I have 2 parameters. These are date parameters.
I want to get parameters from the users.
The records will be selected for the date in the parameters field.
But if the date in the parameters are NULL then the record selection will be for the previous month.
Has anyone encountered this situation ??
Thanks in advance ..

Answer 1

From Crystal reports, I want to pass NULL value in the parameter as a DEFAULT.
I know its not possible, so I passed following date 01/01/1900 in both Date parameters as default.
Then in my select query I said -
select * from purchase
where
     paymentmethod ='Credit Card'
     and
          purchasedatetime >=
          Case {?PurchaseDateFrom}
          when TO_DATE('01/01/1900','dd/mm/yyyy') then SYSDATE-30
          Else {?PurchaseDateFrom}
          End
          and
          purchasedatetime <=
          Case {?PurchaseDateTo}
          when TO_DATE('01/01/1900','dd/mm/yyyy') then  SYSDATE+1
          Else {?PurchaseDateTo}
          End
The above query works fine.
But I want to try something like this - (pseudocode)
first I will check the parameter value :
Declare - myFromDate , myFromTo as variable
If {?PurchaseDateFrom} is null then myFromDate = SYSDATE-30
else myFromDate = {?PurchaseDateFrom}
if {?PurchaseDateTo} is null then myFromTo = SYSDATE+1
else myFromTo = {?PurchaseDateTo}
select * from purchase
where
     paymentmethod ='Credit Card'
     and
     purchasedatetime between myFromDate and myFromTo
Thanks,