Re: adding columns with defaults is not implemented

On Thu, 2005-06-02 at 17:47 -0400, Marcelo wrote:
> Hi,
> Thanks for your reply, but I have some doubts.
>
> Are yoy sugesting I create the column as an Integer then change it to
> Serial? in Pgsql 7 you cant change a column type.
>
> If I create the column as an int then add a default value, how can I make
> this default value increment with each insert?
>
> Thanks again for your help.
> Marcelo
>
>
> ----- Original Message -----
> From: "Scott Marlowe" <smarlowe(at)g2switchworks(dot)com>
> To: "Marcelo" <marcelo(at)humano2(dot)com>
> Cc: <pgsql-general(at)postgresql(dot)org>
> Sent: Thursday, June 02, 2005 4:43 PM
> Subject: Re: [GENERAL] adding columns with defaults is not implemented
>
>
> > On Thu, 2005-06-02 at 15:29, Marcelo wrote:
> > > Hello,
> > > Using Postgres 7.4, I am trying to perform an "alter table
> > > temptable add column "myCol" serial"
> > >
> > > It gives the following msg
> > > ERROR: adding columns with defaults is not implemented
> > >
> > > You cannot add a column that is serial in a table which already has
> > > data in postgres 7.
> > >
> > > Is there a way I can create a serial column on a table which already
> > > has data? Or is the only solution upgrading to postgres 8 ?
> >
> > You can add a default after you add the column with a separate alter
> > table statement...
> >
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[Bottom posting to the top-posted reply] ....

You would have to do this in steps: Assuming that "mytable" exists and
"mycol" is currently of type int and currently has as its max value 100:

create sequence mytable_mycol_seq start with 101;
alter table mytable alter mycol set default
nextval('mytable_mycol_seq'::text);

At this point any new inserts will start autoincrementing the mycol
field starting with value 101.

Sven