Updating database records in a loop?

Question

declare
begin
  for i in (select * from emp)
  loop
    if i.sal=1300 then
      update emp
      set sal=13000;
    end if;
  end loop;
end;

This code

Answer 1

Whenever you can do the update with one single statement, you should do that instead of using a loop. You'll get a very huge performance gain that way; or, the other way round, updates in a loop cost you a lot of performance.

If you really really have to use a loop, of course you need a where condition to make sure you are only updating the record you really want to update. A possible way that always works (even if there is no unique key available) is to use the rowid pseudocolumn:

begin
  for i in (select rowid, emp.* from emp)
  loop
    if i.sal=1300 then
      update emp
      set sal=13000
      where rowid=i.rowid;
    end if;
  end loop;
end;

Another possibility would be using an explicit cursor and the "update ... where current of cursorname" syntax.