Обсуждение: 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...

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@g2switchworks.com>
To: "Marcelo" <marcelo@humano2.com>
Cc: <pgsql-general@postgresql.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...
>
> ---------------------------(end of broadcast)---------------------------
> TIP 2: you can get off all lists at once with the unregister command
>     (send "unregister YourEmailAddressHere" to majordomo@postgresql.org)

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@g2switchworks.com>
> To: "Marcelo" <marcelo@humano2.com>
> Cc: <pgsql-general@postgresql.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...
> >
> > ---------------------------(end of broadcast)---------------------------
> > TIP 2: you can get off all lists at once with the unregister command
> >     (send "unregister YourEmailAddressHere" to majordomo@postgresql.org)
>
>
> ---------------------------(end of broadcast)---------------------------
> TIP 3: if posting/reading through Usenet, please send an appropriate
>       subscribe-nomail command to majordomo@postgresql.org so that your
>       message can get through to the mailing list cleanly

[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

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.

Serial is not a real data type. Do this.

create table foo (bar integer not null);
create sequence foo_bar_seq;
alter table foo alter column bar set default nextval('foo_bar_seq');

Sincerely,

Joshua D. Drake


>
> 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@g2switchworks.com>
> To: "Marcelo" <marcelo@humano2.com>
> Cc: <pgsql-general@postgresql.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...
>>
>>---------------------------(end of broadcast)---------------------------
>>TIP 2: you can get off all lists at once with the unregister command
>>    (send "unregister YourEmailAddressHere" to majordomo@postgresql.org)
>
>
>
> ---------------------------(end of broadcast)---------------------------
> TIP 3: if posting/reading through Usenet, please send an appropriate
>       subscribe-nomail command to majordomo@postgresql.org so that your
>       message can get through to the mailing list cleanly


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"Marcelo" <marcelo@humano2.com> writes:

> 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 ?

I think you can do it as a three-step process:

1) Add the column as an "int" (or "int8") with no default
2) Create the sequence for the column by hand
3) Do ALTER TABLE foo ALTER COLUMN "myCol" DEFAULT nextval('myseq');

This definitely works in 8.0.X and I think it should work in 7.4.X as
well.

A serial column is basically just syntactic sugar for the above, so
you're not losing anything.

-Doug

On Thu, Jun 02, 2005 at 16:57:14 -0400,
  Douglas McNaught <doug@mcnaught.org> wrote:
>
> A serial column is basically just syntactic sugar for the above, so
> you're not losing anything.

In recent versions of postgres, I do think you lose something. I don't
believe the dependency will get tracked as it would for a serial
column (though this is really a bug that should eventually get fixed).
pg_get_serial_sequence will probably not work as well.