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Subject: Re: JSON Path and GIN Questions
From: "David E. Wheeler" <david@justatheory.com>
In-Reply-To: <3826235.1694824574@sss.pgh.pa.us>
Date: Sat, 16 Sep 2023 13:43:47 -0400
Cc: pgsql-hackers@lists.postgresql.org
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To: Tom Lane <tgl@sss.pgh.pa.us>
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On Sep 15, 2023, at 20:36, Tom Lane <tgl@sss.pgh.pa.us> wrote:

> I think that that indicates that you're putting the info in the
> wrong place.  Perhaps the right answer is to insert something
> more explicit in section 11.2, which is the first place where
> we really spend any effort discussing what can be indexed.

Fair enough. How =E2=80=99bout this?

--- a/doc/src/sgml/indices.sgml
+++ b/doc/src/sgml/indices.sgml
@@ -120,7 +120,7 @@ CREATE INDEX test1_id_index ON test1 (id);
    B-tree, Hash, GiST, SP-GiST, GIN, BRIN, and the extension <link
    linkend=3D"bloom">bloom</link>.
    Each index type uses a different
-   algorithm that is best suited to different types of queries.
+   algorithm that is best suited to different types of queries and =
operators.
    By default, the <link linkend=3D"sql-createindex"><command>CREATE
    INDEX</command></link> command creates
    B-tree indexes, which fit the most common situations.
@@ -132,6 +132,14 @@ CREATE INDEX <replaceable>name</replaceable> ON =
<replaceable>table</replaceable>
 </programlisting>
   </para>

+  <note>
+    <para>
+    Only operators on indexed columns are considered as index =
qualifications.
+    Functions never qualify for index usage, aside from
+    <link linkend=3D"indexes-expressional">indexes on =
expressions</link>.
+    </para>
+  </note>
+
   <sect2 id=3D"indexes-types-btree">
    <title>B-Tree</title>


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