| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Kouhei Kaigai <kaigai(at)ak(dot)jp(dot)nec(dot)com> |
| Cc: | Etsuro Fujita <fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp>, Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp>, "tgl(at)sss(dot)pgh(dot)pa(dot)us" <tgl(at)sss(dot)pgh(dot)pa(dot)us>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>, "shigeru(dot)hanada(at)gmail(dot)com" <shigeru(dot)hanada(at)gmail(dot)com> |
| Subject: | Re: Foreign join pushdown vs EvalPlanQual |
| Date: | 2015-12-01 16:54:46 |
| Message-ID: | CA+TgmobOT2zhVE-N5jPKt5Nn3YkoD-1n_b4pTZs1BVeHaHdfqw@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Fri, Nov 27, 2015 at 1:25 AM, Kouhei Kaigai <kaigai(at)ak(dot)jp(dot)nec(dot)com> wrote:
>> Sorry, I don't understand this. In my understanding, fdw_recheck_quals
>> can be defined for a foreign join, regardless of the join type,
>>
> Yes, "can be defined", but will not be workable if either side of
> joined tuple is NULL because of outer join. SQL functions returns
> NULL prior to evaluation, then ExecQual() treats this result as FALSE.
> However, a joined tuple that has NULL fields may be a valid tuple.
>
> We don't need to care about unmatched tuple if INNER JOIN.
This is a really good point, and a very strong argument for the design
KaiGai has chosen here.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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