In SQ02 you can add some code, if it doesn't allow JOIN between tables due to discrepancies between key field.
Define DRAD as an additional structure WDRAD type DRAD (in additional fields)
Right click on it and select Structure code
Add a small code like
DATA w_objky TYPE drad-objk. clead w_drad. w_objky = mara-matnr. * Add other keys if required e.g. DOKAR SELECT SINGLE * INTO w_drad FROM drad WHERE objky EQ w_objky AND dokob EQ 'MARA'.
Regards,
Raymond