| From: | Andy Fan <zhihui(dot)fan1213(at)gmail(dot)com> |
|---|---|
| To: | PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
| Subject: | prerequisites of pull_up_sublinks |
| Date: | 2021-04-21 02:55:29 |
| Message-ID: | CAKU4AWrmgivKLsrxQtgcyfMkgCTRh-AbLfyawQUzgQQgr_PCUQ@mail.gmail.com |
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| Lists: | pgsql-hackers |
Hi,
I'm reading the pull_up_sublinks, and find the below comments.
* However, this optimization *only*
* works at the top level of WHERE or a JOIN/ON clause, because we cannot
* distinguish whether the ANY ought to return FALSE or NULL in cases
* involving NULL inputs. Also, in an outer join's ON clause we can only
* do this if the sublink is degenerate (ie, references only the nullable
* side of the join).
I tried to write some SQLs but still can't understand the above comments.
Any
help here?
--
Best Regards
Andy Fan (https://www.aliyun.com/)
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