How to update database table with key field?

Question

Hello Experts,
I have a database table with following fields
MATNR   - Key
SSOUR  -  Key
KUNNR   - Key
MENG1 
MENG2
MENG3
And this table contains records like...
MSD50001     R      1000001     5.30    2.30    5.25
MSD50002     R      1000002     5.30    2.30    5.25
MSD50003     R      1000003     5.30    2.30    5.25
MSD50005     R      1000004     5.30    2.30    5.25
MSD50004     R      1000005     5.30    2.30    5.25
I have an internal table with same fields of above database table.
MSD50001     A      1000001     5.30    2.30    5.25
MSD50002     A      1000002     5.30    2.30    5.25
MSD50003     A      1000003     5.30    2.30    5.25
MSD50005     A      1000004     5.30    2.30    5.25
MSD50004     A      1000005     5.30    2.30    5.25
MSD50006     A      1000006     5.30    2.30    5.25
I want to update the DB table with following internal table records.
If internal table records = db table records are same then Update....else insert from internal table to db table.
But here, SSOUR is key field so i am not able to use
MODIFY dbtab from itab.
It results me , entries in internal table are inserted into db table.
So i have double records.
Is there any statement which updates the key field? and if no fields in db table then insert it?
Regards
RH

Answer 1

hi,
u cannot update akey field.u can update only non key fields by using key field as a selection criteria.For example if u go to sm30 if u enter any table for inserting values, the key field will always be greyed out it is not succumbed to chnges.but u can insert value into ,if ur inserting and in the insert staemnet if  u have key field which is already present in the table it will return sy-subrc = 4 otherwise it will insert the record and return 0.
eg for update :
UPDATE zdm_wtyprof  SET upload_status = 'S'
                         WHERE spart = wa_upd-spart.
here spart is the key field and it will update the status field in the table as S.
if updated succesfully it will return 0.
SIMILARLY U CAN USE select.