I found it
http://archives.postgresql.org/pgadmin-support/2012-07/msg00007.php
2012/8/23 Dave Page <dpage@pgadmin.org>:
> On Thu, Aug 23, 2012 at 7:19 AM, Timon <timosha@gmail.com> wrote:
>> attached patch fixes SQL of column in SQL pane.
>> sql should be like
>> ALTER TABLE table ADD COLUMN tms timestamp without time zone NOT NULL
>> DEFAULT now();
>> and not
>> ALTER TABLE table ADD COLUMN tms timestamp without time zone;
>> ALTER TABLE table ALTER COLUMN tms SET NOT NULL;
>> ALTER TABLE table ALTER COLUMN tms SET DEFAULT now();
>>
>> it avoids not null constraint problem when you add column to existing
>> table with some data
>
> I can't find the references in the archives (I'm sure this has come up
> before), but iirc, we intentionally didn't do this as it wouldn't be
> clear to the user that despite they might be about to cause a huge
> write. I'm sure there was more to it than that, but my Google-fu is
> failing me at the moment.
>
>
>
> --
> Dave Page
> Blog: http://pgsnake.blogspot.com
> Twitter: @pgsnake
>
> EnterpriseDB UK: http://www.enterprisedb.com
> The Enterprise PostgreSQL Company
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