Thread: adding columns with defaults is not implemented
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 ?
Thanks
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.