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

diff --git a/doc/src/sgml/queries.sgml b/doc/src/sgml/queries.sgml
index 92e54067c99e66fef70d098918c5d9ec4ffed1f1..5adba0af33fd00fe1d8d95c000ce97656ae8a6dd 100644 (file)
--- 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 ac84022c01fc092a0bd5f0fa7af65d75217ad0e3..95f23219746ddc2ee9d409e46b75a20b18c76ec0 100644 (file)
--- 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>