Dbtab Getting Cleared

Question

Hi All
  I am using one Y table for generation of numbers. This table stores the last no generated for a particular combination. But anyhow this table is getting reset and am unable to find the cause.
When i wnt through the coding, i found it ok. First the max value is being selected from the table and after all the opearation is been done, the dbtab is being modified from an itab of the same structure.
There is also a check if no number is found. In that case it'll throw an error message.
Still then am unable to find the cause.
I am using Modify statement along with commit work if modification is a success else rollback work.
Need suggestions urgently.
With Regards
Pradipta K. Mishra

Answer 1

But if am not wrong then Insert will created more than one line item in the table which is not my requirement. My table is to contain only the last generated number.
Code is like :
Fetching the max no.
Select max ( no )
from dbtab
into w_var
where <condn> .
if sy-subrc <> 0.
    message e024.
endif.
Then after doing the necessary operation,
wa_itab-no = w_var1.
append wa_itab to itab.
Modify dbtab from table itab.
if sy-subrc = 0 .
commit work.
else.
rollback work.
endif.