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doc PG 18 relnotes: add GROUP BY column elimination item

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With a nod to PG 9.6.

Reported-by: jian he

Discussion: https://postgr.es/m/CACJufxEqs=EXZETwtaOooTFhZrtxvSWg8M2uPfzjNtS3wQ6Dzw@mail.gmail.com
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Bruce Momjian 2025-05-03 12:57:18 -04:00
parent 04b269da56
commit 24987c6f06
1 changed files with 17 additions and 0 deletions
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17
doc/src/sgml/release-18.sgml
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@ -284,6 +284,23 @@ This optimization can be disabled using enable_distinct_reordering.
</para> </para>
</listitem> </listitem>
<!--
Author: David Rowley <drowley@postgresql.org>
2024-12-12 [bd10ec529] Detect redundant GROUP BY columns using UNIQUE indexes
-->
<listitem>
<para>
Ignore GROUP BY columns that are functionally dependent on other columns (Zhang Mingli, Jian He, David Rowley)
<ulink url="&commit_baseurl;bd10ec529">&sect;</ulink>
</para>
<para>
If a GROUP BY clause includes all columns of a unique index, as well as other columns of the same table, those other columns are redundant and can be dropped
from the grouping. This was already true for non-deferred primary keys.
</para>
</listitem>
<!-- <!--
Author: Richard Guo <rguo@postgresql.org> Author: Richard Guo <rguo@postgresql.org>
2024-10-09 [67a54b9e8] Allow pushdown of HAVING clauses with grouping sets 2024-10-09 [67a54b9e8] Allow pushdown of HAVING clauses with grouping sets