| From: | "David E(dot) Wheeler" <david(at)kineticode(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Marko Tiikkaja <marko(dot)tiikkaja(at)cs(dot)helsinki(dot)fi>, David Fetter <david(at)fetter(dot)org>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: wCTE behaviour |
| Date: | 2010-11-11 17:44:07 |
| Message-ID: | 42E14D00-2530-4C6B-A3A0-113648D84D5F@kineticode.com |
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| Lists: | pgsql-hackers |
On Nov 11, 2010, at 9:29 AM, Tom Lane wrote:
>> I can see that, but if one can't see the result of the write, or can't determine whether or not it will be visible in advance, what's the point of writeable CTEs?
>
> The writeable CTE returns a RETURNING set, which you can and should use
> in the outer query. The thing that is being argued about here is what
> you see if you look "directly" at the target table rather than making
> use of RETURNING. Essentially, I'm arguing that we shouldn't promise
> any particular behavior at that level, just as we don't promise that
> UPDATE updates different rows in any determinate order.
Yes, if RETURNING guarantees the execution order, then great. That was the first thing I tried to do before I realized that the current CTE implementation doesn't support w.
David
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