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 5cc6dbce11b16b495690f2f22c31fad46327e2e2..b851d134b72b8eec21ae24189b9b8ea8ed26dab8 100644 (file)
--- a/doc/src/sgml/queries.sgml
+++ b/doc/src/sgml/queries.sgml
@@ -393,8 +393,8 @@ FROM table_reference , table_r
         consisting of all column names that appear in both
         input tables.  As with USING, these columns appear
         only once in the output table.  If there are no common
-        column names, NATURAL behaves like
-        CROSS JOIN.
+        column names, NATURAL JOIN behaves like
+        JOIN ... ON TRUE, producing a cross-product join.
        
 
        

diff --git a/doc/src/sgml/ref/select.sgml b/doc/src/sgml/ref/select.sgml
index 211e4c320ce3ab87e114841bb427d9615e7b699d..57f11e66fb6dfa42706f8f216aba8c9e888aa955 100644 (file)
--- a/doc/src/sgml/ref/select.sgml
+++ b/doc/src/sgml/ref/select.sgml
@@ -603,9 +603,12 @@ TABLE [ ONLY ] table_name [ * ]
      
       NATURAL
       
-       NATURAL is shorthand for a
+       
+        NATURAL is shorthand for a
         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, NATURAL is equivalent
+        to ON TRUE.