Обсуждение: Add a serial column to a table based on a sort clause

I have a table, which has a creation_ts (timestamp) column, but does not
have a id (serial) column. I want to add such a one, but, AFAIK, if I enter

ALTER TABLE table ADD COLUMN id serial

it will randomly put the sequence numbers.

I wrote a function, which uses a cursor and UPDATE WHERE CURRENT OF, and
it works, but is there any other, more "elegant", way?

CREATE OR REPLACE FUNCTION newsfeed_seq_add_cursor
() RETURNS void AS $$
    DECLARE
        curs refcursor;
        rec record;
    BEGIN
        create sequence seq;
        ALTER TABLE table ADD COLUMN id int;
        OPEN curs FOR SELECT * FROM table ORDER BY creation_ts FOR UPDATE;
        FETCH curs INTO rec;
        WHILE FOUND IS TRUE
        LOOP
            UPDATE table SET id = nextval('seq') WHERE CURRENT OF curs;
        END LOOP;
        ALTER TABLE table ALTER COLUMN id SET NOT NULL, ALTER COLUMN id
SET DEFAULT nextval('seq');
    END;
$$ language plpgsql;

On Wed, Sep 02, 2009 at 04:40:13PM +0400, Igor Katson wrote:
> I have a table, which has a creation_ts (timestamp) column, but does
> not have a id (serial) column. I want to add such a one, but, AFAIK,
> if I enter
>
> ALTER TABLE table ADD COLUMN id serial
>
> it will randomly put the sequence numbers.

"Random" is how you should think of them.  Sequences guarantee only
uniqueness.  Neither order nor gap-less numbers, nor any other
property apply to them.

Cheers,
David.
--
David Fetter <david@fetter.org> http://fetter.org/
Phone: +1 415 235 3778  AIM: dfetter666  Yahoo!: dfetter
Skype: davidfetter      XMPP: david.fetter@gmail.com

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