From 5512427b19e79ac95535e7c942bd479db807f7be Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Thu, 20 Jul 2017 12:41:26 -0400
Subject: [PATCH] Doc: clarify description of degenerate NATURAL joins.

Claiming that NATURAL JOIN is equivalent to CROSS JOIN when there are
no common column names is only strictly correct if it's an inner join;
you can't say e.g. CROSS LEFT JOIN.  Better to explain it as meaning
JOIN ON TRUE, instead.  Per a suggestion from David Johnston.

Discussion: https://postgr.es/m/CAKFQuwb+mYszQhDS9f_dqRrk1=Pe-S6D=XMkAXcDf4ykKPmgKQ@mail.gmail.com
---
 doc/src/sgml/queries.sgml    | 4 ++--
 doc/src/sgml/ref/select.sgml | 7 +++++--
 2 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/doc/src/sgml/queries.sgml b/doc/src/sgml/queries.sgml
index 5cc6dbce11..b851d134b7 100644
--- a/doc/src/sgml/queries.sgml
+++ b/doc/src/sgml/queries.sgml
@@ -393,8 +393,8 @@ FROM <replaceable>table_reference</replaceable> <optional>, <replaceable>table_r
         consisting of all column names that appear in both
         input tables.  As with <literal>USING</>, these columns appear
         only once in the output table.  If there are no common
-        column names, <literal>NATURAL</literal> behaves like
-        <literal>CROSS JOIN</literal>.
+        column names, <literal>NATURAL JOIN</literal> behaves like
+        <literal>JOIN ... ON TRUE</literal>, producing a cross-product join.
        </para>
 
        <note>
diff --git a/doc/src/sgml/ref/select.sgml b/doc/src/sgml/ref/select.sgml
index 211e4c320c..57f11e66fb 100644
--- a/doc/src/sgml/ref/select.sgml
+++ b/doc/src/sgml/ref/select.sgml
@@ -603,9 +603,12 @@ TABLE [ ONLY ] <replaceable class="parameter">table_name</replaceable> [ * ]
      <varlistentry>
       <term><literal>NATURAL</literal></term>
       <listitem>
-       <para><literal>NATURAL</literal> is shorthand for a
+       <para>
+        <literal>NATURAL</literal> is shorthand for a
         <literal>USING</> list that mentions all columns in the two
-        tables that have the same names.
+        tables that have matching names.  If there are no common
+        column names, <literal>NATURAL</literal> is equivalent
+        to <literal>ON TRUE</>.
        </para>
       </listitem>
      </varlistentry>