Re: Document efficient self-joins / UPDATE LIMIT techniques.

>
> I have changed the status of commitfest entry to "Returned with
> Feedback" as Laurenz's comments have not yet been resolved. Please
> handle the comments and update the commitfest entry accordingly.
>
>
Here's another attempt, applying Laurenz's feedback:

I removed all changes to the SELECT documentation. That might seem strange
given that the heavy lifting happens in the SELECT, but I'm working from
the assumption that people's greatest need for a ctid self-join will be
because they are trying to find the LIMIT keyword on UPDATE/DELETE and
coming up empty.

Because the join syntax is subtly different between UPDATE and DELETE, I've
kept code examples in both, but the detailed explanation is in UPDATE under
the anchor "update-limit" and the DELETE example links to it.