Doc: clarify description of degenerate NATURAL joins.

tglsfdc · tglsfdc · commit a6088e1f5a58 · 2017-07-20T12:41:45.000-04:00
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
@@ -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
@@ -494,9 +494,12 @@ 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>
