Data visibility for returning statement

On Sat, Apr 26, 2025 at 5:50 AM PG Doc comments form <noreply@postgresql.org>
wrote:

The following documentation comment has been logged on the website:

Page: https://www.postgresql.org/docs/17/dml-returning.html
Description:

Today I found a pretty special use-case for the "RETURNING" functionality,
which I cannot find documentation for?
If you have a statement as follows:
UPDATE persons SET name = 'Bob' WHERE id = 4
RETURNING (SELECT name FROM persons WHERE id = 4)
The returning data will be whatever the value was before the row was
modified. This differs from if I were to "RETURNING name". I found this to
be interesting and could possibly warrant some kind of explanation in the
documentation?

I would not want to encourage that form of query. The novelty is more
problematic than the brevity. Plus, repetition.

with new_p as ( update persons set name = 'Bob' returning name where id = 4)
select
old_p.id as id,
old_p.name as old_name,
new_p.name as new_name
from persons as old_p
join new_p on new_p.id = old_p.id

And now that we actually allow references to "new" and "old" in v18 that
form is also obsolete and you can do this directly.

David J.