To find total count based on Date values

Dear Friends,

My Bex query is based on Infoset (DSO1). In the ROWS I have only one field ZNOT_TYP. Input Parameter Range - ZCRT_DAT

I have 3 date fields in my Infoset.

ZCRT_DAT - Creation Date

ZNOT_DAT - Notification Date

ZCHN_DAT - Changed on Date

Column 1 - Logic: If ZNOT_DAT  is not empty and falls under the ZCRT_DAT(User input Range) then take the count.  If ZNOT_DAT is empty then check ZCHN_DAT, If ZCHN_DAT value falls under the input field ZCRT_DAT take the count.  If already data is available in ZNOT_DAT no need to check ZCHN_DAT.

Also please suggest whether i have to create a formula or CKF for column one field.

Thanks

Vijay