How to generate unique numbers

Question

hi all,
I want to generate unique numbers always starting from 1 using a single sql query and I dont want to use a sequence and i dont think rownum will be helpful for generating unique numbers in all cases . how to do this ?
thanks & regards,
kumar.

Answer 1

If two users get the MAX from temp, they would be updating with the same value for two different rows.If TEMP is a genuine temporary table, this is not an issue, because the data in a temporary table is only visible within a session.
The big problem with this approach is the mutating table one: we cannot issue the requisite select statement from a BEFORE INSERT trigger. So this solution is only going to work with a view and an INSTEAD OF INSERT trigger.
Another, more workable, solution is to use a code control table. This can be (should be) another temporary table, with one row holding one column - next value for TEMP.ID. Normally we would rule out such a solution because it serializes access to the inserted table, but as this is only on a per session basis, it doesn't matter.
CREATE OR REPLACE TRIGGER tmp_bir BEFORE INSERT ON temp1 FOR EACH ROW
DECLARE
  ln NUMBER;
BEGIN
  SELECT nvl(code1.next_id,1) INTO ln
  FROM code1;
  :NEW.id := ln;
  UPDATE code1
  SET    next_id := ln+1;
END;Beware: coded freehand, so may need debugging.
Cheers, APC