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From: Amit Langote <[email protected]>
To: Tom Lane <[email protected]>
Cc: Postgres General <[email protected]>
Subject: Re: Table Rewrite During ALTER TABLE ... ADD COLUMN ... DEFAULT NULL
Date: Thu, 3 Apr 2014 13:26:45 +0900
Message-ID: <CA+HiwqGbTA1RNxngDYxeHQVr6zeu2vF30fK7z_bexg-KW+PYRw@mail.gmail.com> (raw)
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On Thu, Apr 3, 2014 at 1:19 PM, Tom Lane <[email protected]> wrote:
> Amit Langote <[email protected]> writes:
>> On Thu, Apr 3, 2014 at 12:54 PM, Tom Lane <[email protected]> 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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