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From: Tom Lane <[email protected]>
To: Amit Langote <[email protected]>
Cc: Postgres General <[email protected]>
Subject: Re: Table Rewrite During ALTER TABLE ... ADD COLUMN ... DEFAULT NULL
Date: Wed, 02 Apr 2014 23:54:32 -0400
Message-ID: <[email protected]> (raw)
In-Reply-To: <CA+HiwqE35_+z0_gFw9mp=_0MLgPfb=+QY910LG7C-sBNTvqdgg@mail.gmail.com>
References: <CA+HiwqE35_+z0_gFw9mp=_0MLgPfb=+QY910LG7C-sBNTvqdgg@mail.gmail.com>
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Amit Langote <[email protected]> writes:
> When I do the following:

> ALTER TABLE table ADD COLUMN numeric(x) DEFAULT NULL;

> The table is rewritten whereas notes section on the manual page for
> ALTER TABLE says otherwise (which holds true for most of the cases
> though).

Try it without the explicit DEFAULT clause.

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.

			regards, tom lane


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