Date: Mon, 8 Dec 2025 19:39:52 +0100
From: Erik Wienhold <ewie@ewie.name>
To: andy.hardin@gmail.com, pgsql-docs@lists.postgresql.org
Subject: Re: Virtual Generated Columns
Message-ID: <ee6ab73a-ba54-4f02-bbad-47eeb3cff162@ewie.name>
References: <176494306051.2921398.8686936183868575892@wrigleys.postgresql.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: 
 <176494306051.2921398.8686936183868575892@wrigleys.postgresql.org>
Archived-At: 
 <https://www.postgresql.org/message-id/ee6ab73a-ba54-4f02-bbad-47eeb3cff162%40ewie.name>
Precedence: bulk

On 2025-12-05 14:57 +0100, PG Doc comments form wrote:
> The following documentation comment has been logged on the website:
> 
> Page: https://www.postgresql.org/docs/17/ddl-generated-columns.html
> Description:
> 
> The documentation for generated columns in PostgreSQL versions prior to 18
> mention "virtual" columns, but as far as I can tell, this is not available
> prior to 18.
> 
> In v17, this is just in the first paragraph.
> 
> > A generated column is a special column that is always computed from other
> columns. Thus, it is for columns what a view is for tables. There are two
> kinds of generated columns: stored and virtual. A stored generated column is
> computed when it is written (inserted or updated) and occupies storage as if
> it were a normal column. A virtual generated column occupies no storage and
> is computed when it is read. Thus, a virtual generated column is similar to
> a view and a stored generated column is similar to a materialized view
> (except that it is always updated automatically). PostgreSQL currently
> implements only stored generated columns.

The last sentence correctly states that Postgres v17- does not implement
virtual columns.  The paragraph is meant as a general overview because
other RDBMS at that time had already implemented both flavors, e.g.
SQLite.

-- 
Erik Wienhold