Re: support ALTER COLUMN SET EXPRESSION over virtual generated column with check constraint

From: "Matheus Alcantara" <matheusssilv97(at)gmail(dot)com>
To: "jian he" <jian(dot)universality(at)gmail(dot)com>, "Matheus Alcantara" <matheusssilv97(at)gmail(dot)com>
Cc: "PostgreSQL Hackers" <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: support ALTER COLUMN SET EXPRESSION over virtual generated column with check constraint
Date: 2026-01-20 18:48:11
Message-ID: DFTN32P3FIIG.DMEXA0C6V6QG@gmail.com
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On Mon Jan 19, 2026 at 1:11 PM -03, jian he wrote:
> I ultimately settled on the following:
> + Replacing the expression of a virtual generated columns do not require a
> + table rewrite, however if the column is part of a
> <literal>CHECK</literal>
> + constraint expression, the constraint will be rebuilt, requiring a table
> + scan to ensure that existing rows meet the constraint.
>
Thanks for the new version. Just a minor comment

+ Replacing the expression of a virtual generated columns do not require a
+ table rewrite, however if the column is part of a <literal>CHECK</literal>
+ constraint expression, the constraint will be rebuilt, requiring a table
+ scan to ensure that existing rows meet the constraint.

I think that it sounds better with: "Replacing the expression of a
virtual generated column does not require a table rewrite..."

--
Matheus Alcantara
EDB: https://www.enterprisedb.com

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