update nested select locking?

Could someone please settle an disagreement:

Is the following an atomic operation or is dirty data possible:

create tbl
(
col number;
);

insert into tbl values (0);

update tbl set col = (select sum(col + 1) from tlb where rownum = 1);

Or does it need to be in a transaction? Or should a "for update" be used.

Thank you. Received on Thu Jul 27 2006 - 09:39:42 CDT