From: | Andrey Lepikhov <a(dot)lepikhov(at)postgrespro(dot)ru> |
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To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
Subject: | Re: Optimization issue of branching UNION ALL |
Date: | 2022-12-22 11:59:41 |
Message-ID: | 628db719-9c26-7aa3-540d-9b6d68e68da6@postgrespro.ru |
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Lists: | pgsql-hackers |
On 22/12/2022 06:50, Tom Lane wrote:
>> 2. Iterative passes along the append_rel_list for replacing vars in the
>> translated_vars field. I can't grasp real necessity of passing all the
>> append_rel_list during flattening of an union all leaf subquery. No one
>> can reference this leaf, isn't it?
>
> After thinking about that for awhile, I believe we can go further:
> the containing_appendrel is actually the *only* part of the upper
> query that needs to be adjusted. So we could do something like
> the attached.
>
> This passes check-world, but I don't have quite enough confidence
> in it to just commit it.
Thanks, I have written the letter because of some doubts too. But only
one weak point I could imagine - if someday sql standard will be changed.
Your code looks better, than previous attempt.
--
regards,
Andrey Lepikhov
Postgres Professional
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