postgres.git / summary / log / commit / refs

commit    ed3dc224e5aabd3cb0a5c348107f973fe5b10b0d
Author:   Tom Lane <tgl@sss.pgh.pa.us>
Date:     Thu Jul 20 16:41:26 2017 +0000
First released in: 10.0, 9.2.22, 9.3.18, 9.4.13, 9.5.8, 9.6.4

    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 30792f45f15..0588da2912c 100644
--- a/doc/src/sgml/queries.sgml
+++ b/doc/src/sgml/queries.sgml
@@ -391,8 +391,8 @@ 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 211e4c320ce..57f11e66fb6 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>


[parent: eb145fdfea91]