| From: | Marko Tiikkaja <marko(dot)tiikkaja(at)cs(dot)helsinki(dot)fi> |
|---|---|
| To: | David Fetter <david(at)fetter(dot)org> |
| Cc: | Yeb Havinga <yebhavinga(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: wCTE behaviour |
| Date: | 2010-11-13 14:22:17 |
| Message-ID: | 9D024E93-80D2-42FC-952F-9D5F15ECFB9B@cs.helsinki.fi |
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| Lists: | pgsql-hackers |
On 13 Nov 2010, at 15:41, David Fetter <david(at)fetter(dot)org> wrote:
> On Sat, Nov 13, 2010 at 02:28:35PM +0100, Yeb Havinga wrote:
>> On 2010-11-12 16:51, David Fetter wrote:
>>> On Fri, Nov 12, 2010 at 10:25:51AM -0500, Tom Lane wrote:
>>>>
>>>> Yeah, that's another interesting question: should we somehow force
>>>> unreferenced CTEs to be evaluated anyhow?
>>> Yes.
>> After a night's sleep I'm still thinking no. Arguments:
>> 1) the name "Common Table Expression" suggests that t must be
>> regarded as an expression, hence syntactically / proof theoretic and
>> not as a table, set of rows / model theoretic. I.e. it is not a
>> "Common Table".
>
> Disagree. A table never referred to in a query still exists.
> Similarly, if a normal CTE called a data-changing function but was
> nevertheless not referred to, it would still run.
Actually, it wouldn't.
But if we make the behaviour of wCTEs hard(er) to predict, we are
going to have a pretty bad feature in our hands. Let's not repeat our
mistakes, please.
Regards,
Marko Tiikkaja
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