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Date: Wed, 17 Aug 2022 14:58:24 -0400
From: Bruce Momjian <bruce@momjian.us>
To: Jeff Janes <jeff.janes@gmail.com>
Cc: pgsql-docs <pgsql-docs@postgresql.org>
Subject: Re: CREATE INDEX...USING
Message-ID: <Yv06UMdbAdOMySoF@momjian.us>
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On Wed, Aug 17, 2022 at 12:41:03PM -0400, Jeff Janes wrote:
> This was recently added to CREATE INDEX reference page:
> 
> +        The optional <literal>USING</literal> clause specifies an index
> +        type as described in <xref linkend="indexes-types"/>.  If not
> +        specified, a default index type will be used based on the
> +        data types of the columns.
> 
> But I think this is wrong, the default type is BTREE, it does not depend on the
> data type.  Or at least, I've never witnessed the claimed behavior.  The claim
> also conflicts with what is said at https://www.postgresql.org/docs/10/
> indexes-types.html

You are correct --- parser/gram.y has:

	access_method_clause:
	            USING name                              { $$ = $2; }
	            | /*EMPTY*/                             { $$ = DEFAULT_INDEX_TYPE; }
	
and from include/catalog/index.h:

	#define DEFAULT_INDEX_TYPE  "btree"

Patch attached.

-- 
  Bruce Momjian  <bruce@momjian.us>        https://momjian.us
  EDB                                      https://enterprisedb.com

  Indecision is a decision.  Inaction is an action.  Mark Batterson


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diff --git a/doc/src/sgml/ref/create_index.sgml b/doc/src/sgml/ref/create_index.sgml
index 944fdb4b09..cb4b43f637 100644
--- a/doc/src/sgml/ref/create_index.sgml
+++ b/doc/src/sgml/ref/create_index.sgml
@@ -154,9 +154,8 @@ CREATE [ UNIQUE ] INDEX [ CONCURRENTLY ] [ [ IF NOT EXISTS ] <replaceable class=
       <listitem>
        <para>
         The optional <literal>USING</literal> clause specifies an index
-        type as described in <xref linkend="indexes-types"/>.  If not
-        specified, a default index type will be used based on the
-        data types of the columns.
+        type as described in <xref linkend="indexes-types"/>.  The
+        default is <literal>btree</literal>.
        </para>
       </listitem>
      </varlistentry>

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