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| 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 12:41:37 -0400 |
| commit | 315ca7ffb90939af8b3e08f5a2a6afbfc6d89c7d (patch) | |
| tree | 5baa18a8c67c065e91844e94f910d32fb4b715f7 | |
| parent | c2bbec9f2b3672f57be27e20f26db141ab430da8 (diff) | |
| download | postgresql-315ca7ffb90939af8b3e08f5a2a6afbfc6d89c7d.tar.gz | |
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 92e54067c9..5adba0af33 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 ac84022c01..95f2321974 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> |