Oracle - Modify an existing table to auto-increment a column

Question

I have a table with the following column:

NOTEID      NUMBER NOT NULL,

For all intents and purposes, this column is the primary key. This

Answer 1

You can't alter the table. Oracle doesn't support declarative auto-incrementing columns. You can create a sequence

CREATE SEQUENCE note_seq
  START WITH 800
  INCREMENT BY 1
  CACHE 100;

Then, you can create a trigger

CREATE OR REPLACE TRIGGER populate_note_id
  BEFORE INSERT ON note
  FOR EACH ROW
BEGIN
  :new.note_id := note_seq.nextval;
END;

or, if you want to allow callers to specify a non-default NOTE_ID

CREATE OR REPLACE TRIGGER populate_note_id
  BEFORE INSERT ON note
  FOR EACH ROW
BEGIN
  IF( :new.note_id is null )
  THEN 
    :new.note_id := note_seq.nextval;
  END IF;
END;