Re: Data visibility for returning statement

On Sat, Apr 26, 2025 at 5:50 AM PG Doc comments form <noreply(at)postgresql(dot)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.