| From: | Richard Guo <guofenglinux(at)gmail(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Alexander Lakhin <exclusion(at)gmail(dot)com>, Jian Guo <gjian(at)vmware(dot)com>, Tomas Vondra <tomas(dot)vondra(at)enterprisedb(dot)com>, Hans Buschmann <buschmann(at)nidsa(dot)net>, "pgsql-hackers(at)lists(dot)postgresql(dot)org" <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Zhenghua Lyu <zlyu(at)vmware(dot)com> |
| Subject: | Re: Wrong rows estimations with joins of CTEs slows queries by more than factor 500 |
| Date: | 2024-01-08 11:14:11 |
| Message-ID: | CAMbWs49cnL7OcSfiyJ_VEKSYE1L5X7KjhOtVzSmkSauE89pLPQ@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Sun, Jan 7, 2024 at 6:41 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Alexander Lakhin <exclusion(at)gmail(dot)com> writes:
> > Please look at the following query:
> > CREATE TABLE t(i int);
> > INSERT INTO t VALUES (1);
> > VACUUM ANALYZE t;
>
> > WITH ir AS (INSERT INTO t VALUES (2) RETURNING i)
> > SELECT * FROM ir WHERE i = 2;
>
> > which produces ERROR: no relation entry for relid 1
> > starting from f7816aec2.
Nice catch.
> Thanks for the report! I guess we need something like the attached.
+1.
> I'm surprised that this hasn't been noticed before; was the case
> really unreachable before?
It seems that this case is only reachable with Vars of an INSERT target
relation, and it seems that there is no other way to reference such a
Var other than using CTE.
Thanks
Richard
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