From: Tom Lane <tgl@sss.pgh.pa.us>
To: Amit Langote <amitlangote09@gmail.com>
cc: Postgres General <pgsql-general@postgresql.org>
Subject: Re: Table Rewrite During ALTER TABLE ... ADD COLUMN ... DEFAULT NULL
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Comments: In-reply-to Amit Langote <amitlangote09@gmail.com>
 message dated "Thu, 03 Apr 2014 13:12:18 +0900"
Date: Thu, 03 Apr 2014 00:19:36 -0400
Message-ID: <3704.1396498776@sss.pgh.pa.us>
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Amit Langote <amitlangote09@gmail.com> writes:
> On Thu, Apr 3, 2014 at 12:54 PM, Tom Lane <tgl@sss.pgh.pa.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.

			regards, tom lane


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