From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Merlin Moncure <mmoncure(at)gmail(dot)com>, David Fetter <david(at)fetter(dot)org>, Andres Freund <andres(at)anarazel(dot)de>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Changed SRF in targetlist handling |
Date: | 2016-06-06 18:15:56 |
Message-ID: | CA+TgmobYiKbT26398CExrAtjei3nd76TwyYvJ+UTvFr64nNmvg@mail.gmail.com |
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Lists: | pgsql-hackers |
On Mon, Jun 6, 2016 at 11:50 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>> On Mon, May 23, 2016 at 4:15 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>>> 2. Rewrite into LATERAL ROWS FROM (srf1(), srf2(), ...). This would
>>> have the same behavior as before if the SRFs all return the same number
>>> of rows, and otherwise would behave differently.
>
>> I thought the idea was to rewrite it as LATERAL ROWS FROM (srf1()),
>> LATERAL ROWS FROM (srf2()), ...
>
> No, because then you get the cross-product of multiple SRFs, not the
> run-in-lockstep behavior.
Oh. I assumed that was the expected behavior. But, ah, what do I know?
>> The rewrite you propose here seems to NULL-pad rows after the first
>> SRF is exhausted:
>
> Yes. That's why I said it's not compatible if the SRFs don't all return
> the same number of rows. It seems like a reasonable definition to me
> though, certainly much more reasonable than the current run-until-LCM
> behavior.
I can't argue with that.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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