From: | Andy Fan <zhihui(dot)fan1213(at)gmail(dot)com> |
---|---|
To: | Julien Rouhaud <rjuju123(at)gmail(dot)com> |
Cc: | Ashutosh Bapat <ashutosh(dot)bapat(dot)oss(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
Subject: | Re: [PATCH] Erase the distinctClause if the result is unique by definition |
Date: | 2020-02-11 12:14:14 |
Message-ID: | CAKU4AWrHSOGQ0q1wqnGk=kN8o4ZA=9uOyzL0eqY93=VkU4y08A@mail.gmail.com |
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On Tue, Feb 11, 2020 at 3:56 PM Julien Rouhaud <rjuju123(at)gmail(dot)com> wrote:
> >
> > and if we prepare sql outside a transaction, and execute it in the
> > transaction, the other session can't drop the constraint until the
> > transaction is ended.
>
> And what if you create a view on top of a query containing a distinct
> clause
> rather than using prepared statements? FWIW your patch doesn't handle such
> case at all, without even needing to drop constraints:
>
> CREATE TABLE t (a int primary key, b int not null, c int);
> INSERT INTO t VALUEs(1, 1, 1), (2, 2, 2);
> CREATE UNIQUE INDEX t_idx1 on t(b);
> CREATE VIEW v1 AS SELECT DISTINCT b FROM t;
> EXPLAIN SELECT * FROM v1;
> server closed the connection unexpectedly
> This probably means the server terminated abnormally
> before or while processing the request.
>
>
This error can be fixed with
- num_of_rtables = bms_num_members(non_semi_anti_relids);
+ num_of_rtables = list_length(query->rtable);
This test case also be added into the patch.
> I also think this is not the right way to handle this optimization.
>
do you have any other concerns?
Attachment | Content-Type | Size |
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0001-Erase-the-distinctClause-if-the-result-is-unique-by-.patch | application/octet-stream | 33.8 KB |
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