Re: JSON Path and GIN Questions

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 ’bout 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="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="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="indexes-expressional">indexes on expressions</link>.
+    </para>
+  </note>
+
   <sect2 id="indexes-types-btree">
    <title>B-Tree</title>