Most non trivial tables have primary key (THE most important column or columns) that uniquely identifies data in rest of the row. In all but trivial application, you’d want a meaningless auto-incrementing number to take its place. Even when you insert a
autoincrementing number, you’d want the value back for foreign key elsewhere.

Almost all databases that support autoincrement encourage a programmer
to abandon these good DB design norms by allowing an easier option of
creating a fake primary key instead.

By not providing Autoincrement, Oracle is forcing designer to THINK..

And that is THE MOST important advantage, I THINK!!!

/* My table is **/
CREATE TABLE TIME_COMPANY
(
COMPANYID integer NOT NULL ,
COMPANYNAME varchar2 (100) NOT NULL
)

/* And its trigger would be like */
CREATE OR REPLACE TRIGGER TIME_COMPANY_TR
BEFORE INSERT ON TIME_COMPANY
FOR EACH ROW
DECLARE TEMP_NO INT;
BEGIN
SELECT TIME_COMPANY_COMPANYID_SEQ.NEXTVAL INTO :NEW.COMPANYID FROM DUAL;
END;

Regards
Adnan Hashmi.

This won’t work in an envioronment where more than one transaction is open at once. That means you should never ever use it because it’s bad practice and not scalable. (You never really know where it will end up.)

If two users do this at the nerly same time, more specifically if a second user does their insert after the first but before the first user commits, the second commit will fail with a constraint violation. That is, unless the column isn’t unique, in which case you’ll just get duplicate values.