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 1010f0508bc04ed149a6a384d8a2babd82bda5ff..81ccbe6399cb7e2b07bf022fd4a908d6b7a8b352 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 b1727b9807ab8518f9745a71cdd38d8b17c89096..f740a128b164f6deb5d9723efbbafc34e4cd5df8 100644 (file)
--- a/doc/src/sgml/ref/select.sgml
+++ b/doc/src/sgml/ref/select.sgml
@@ -494,9 +494,12 @@ 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.