diff options
| author | Tom Lane <tgl@sss.pgh.pa.us> | 2017-07-20 12:41:26 -0400 |
|---|---|---|
| committer | Tom Lane <tgl@sss.pgh.pa.us> | 2017-07-20 12:41:45 -0400 |
| commit | a6088e1f5a58e47ee6f207ec13c67773852df970 (patch) | |
| tree | 75dff720b634ea2846199e556a0cf0a965467941 | |
| parent | e947838ae432579d86fa35f0b4d6a384c20d4824 (diff) | |
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
| -rw-r--r-- | doc/src/sgml/queries.sgml | 4 | ||||
| -rw-r--r-- | 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 1010f0508bc..81ccbe6399c 100644 --- 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 b1727b9807a..f740a128b16 100644 --- 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> |