Problem in table update.

Hi All.

I am facing one problem while updating the Ztable. The scnerio is like that we are tracking PO changes. So we created one Ztable to store PO changes. In this table we ahve Sr No field as primary key. When user press SAVE button, first maximum Sr No is selected from table and with addition of 1 new record is created with taht PO number. Now problem is that when two users save different PO at same time , them only one entry is saved in table.

Can i use enque deque or any other login I have to use for this?

Thanks.