Limit dynamic parameter list to data added in last month

Question

I have a crystal reports X1 report that uses a dynamic parameter for users to select. This parameter displays all database entries for the field. The field is called PLANNAME and lists out names that users have entered from the main application screens. I want to limit the display of these plan names to the most recent based on the CREATEDATE which is a field on the table that the Planname is stored.
Is there a way that Crystal reports can restrict / limit the list of vaules returned and available for report users to select. The list is steadily growing, and now requires the report users to scroll through hundreds of plannames (that is, all the plan names that have been created over the last two years).
Look forward to any suggestions.
Regards
dave

Answer 1

Just a follow-up on progress ...... which has been a bit slow.
Have got into the Business View Manager and found the vaious parameter levels PLANNAME DC, PLANNAME_BE, PLANNAME_BV, PLANNAME_DF, and added the following filter to the data_foundation: (note: first part is a View I have created, )
{CRYSTALVW_EFTPLANDETAIL.PLANNAME} in LastFullMonth.
I have not been able to add the SQL expression as it errors with reference to the INCORRECT SYNTAX NEAR THE KEYWORD "select"
SELECT DISTINCT PLANNAME, DATECREATED FROM CRYSTALVW_EFTPLANDETAIL WHERE DATECREATED >= '2009-01-01'
Note, this works okat in Enterprise manager Query Analyser, but not in the DF data_foundation.
and the suggestion you made:
SELECT DISTINCT PLANNAME FROM CRYSTALVW_EFTPLANDETAIL WHERE DATECREATED >= DATEADD('m',-1,GETDATE())
This produces the same error message - INCORRECT SYNTAX NEAR THE KEYWORD "select"
and I can not get this to work in Query Analyser - error message is
Server: Msg 1023, Level 15, State 1, Line 2
Invalid parameter 1 specified for dateadd.
I shall continue to work thru this, but would appreciate any helpful hints.
many thanks
Dave