From: | Amit Langote <amitlangote09(at)gmail(dot)com> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Postgres General <pgsql-general(at)postgresql(dot)org> |
Subject: | Re: Table Rewrite During ALTER TABLE ... ADD COLUMN ... DEFAULT NULL |
Date: | 2014-04-03 04:26:45 |
Message-ID: | CA+HiwqGbTA1RNxngDYxeHQVr6zeu2vF30fK7z_bexg-KW+PYRw@mail.gmail.com |
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Lists: | pgsql-docs pgsql-general |
On Thu, Apr 3, 2014 at 1:19 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Amit Langote <amitlangote09(at)gmail(dot)com> writes:
>> On Thu, Apr 3, 2014 at 12:54 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>>> Some experimentation suggests that we are smart about "DEFAULT NULL"
>>> unless the column type requires a length-coercion cast, in which
>>> case the default expression involves a function call, and that doesn't
>>> get elided.
>
>> Is there a warning about such behavior in the manual?
>> Is it useful to include it somewhere (not sure where though)?
>
> We could just rephrase the ALTER TABLE docs to say that the table
> rewrite is avoided if you omit the DEFAULT clause, rather than
> saying that a null default works.
>
Agreed.
--
Amit
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