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doc: split out the NATURAL/CROSS JOIN in SELECT syntax

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This allows the syntax to be more accurate about what clauses are
supported.  Also switch an example query to use the ANSI join syntax.

Reported-by: Joel Jacobson

Discussion: https://postgr.es/m/67b71d3e-0c22-44df-a223-351f14418319@www.fastmail.com

Backpatch-through: 11
This commit is contained in:
Bruce Momjian 2022-08-31 21:46:14 -04:00
parent 1703726488
commit 3e337b585a
1 changed files with 24 additions and 22 deletions
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46
doc/src/sgml/ref/select.sgml
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@ -59,7 +59,9 @@ SELECT [ ALL | DISTINCT [ ON ( <replaceable class="parameter">expression</replac
[ LATERAL ] <replaceable class="parameter">function_name</replaceable> ( [ <replaceable class="parameter">argument</replaceable> [, ...] ] ) AS ( <replaceable class="parameter">column_definition</replaceable> [, ...] )
[ LATERAL ] ROWS FROM( <replaceable class="parameter">function_name</replaceable> ( [ <replaceable class="parameter">argument</replaceable> [, ...] ] ) [ AS ( <replaceable class="parameter">column_definition</replaceable> [, ...] ) ] [, ...] )
[ WITH ORDINALITY ] [ [ AS ] <replaceable class="parameter">alias</replaceable> [ ( <replaceable class="parameter">column_alias</replaceable> [, ...] ) ] ]
<replaceable class="parameter">from_item</replaceable> [ NATURAL ] <replaceable class="parameter">join_type</replaceable> <replaceable class="parameter">from_item</replaceable> [ ON <replaceable class="parameter">join_condition</replaceable> | USING ( <replaceable class="parameter">join_column</replaceable> [, ...] ) [ AS <replaceable class="parameter">join_using_alias</replaceable> ] ]
<replaceable class="parameter">from_item</replaceable> <replaceable class="parameter">join_type</replaceable> <replaceable class="parameter">from_item</replaceable> { ON <replaceable class="parameter">join_condition</replaceable> | USING ( <replaceable class="parameter">join_column</replaceable> [, ...] ) [ AS <replaceable class="parameter">join_using_alias</replaceable> ] }
<replaceable class="parameter">from_item</replaceable> NATURAL <replaceable class="parameter">join_type</replaceable> <replaceable class="parameter">from_item</replaceable>
<replaceable class="parameter">from_item</replaceable> CROSS JOIN <replaceable class="parameter">from_item</replaceable>
<phrase>and <replaceable class="parameter">grouping_element</replaceable> can be one of:</phrase>
@ -600,19 +602,15 @@ TABLE [ ONLY ] <replaceable class="parameter">table_name</replaceable> [ * ]
<listitem>
<para><literal>FULL [ OUTER ] JOIN</literal></para>
</listitem>
<listitem>
<para><literal>CROSS JOIN</literal></para>
</listitem>
</itemizedlist>
For the <literal>INNER</literal> and <literal>OUTER</literal> join types, a
join condition must be specified, namely exactly one of
<literal>NATURAL</literal>, <literal>ON <replaceable
class="parameter">join_condition</replaceable></literal>, or
<literal>ON <replaceable
class="parameter">join_condition</replaceable></literal>,
<literal>USING (<replaceable
class="parameter">join_column</replaceable> [, ...])</literal>.
See below for the meaning. For <literal>CROSS JOIN</literal>,
none of these clauses can appear.
class="parameter">join_column</replaceable> [, ...])</literal>,
or <literal>NATURAL</literal>. See below for the meaning.
</para>
<para>
@ -623,17 +621,9 @@ TABLE [ ONLY ] <replaceable class="parameter">table_name</replaceable> [ * ]
In the absence of parentheses, <literal>JOIN</literal>s nest
left-to-right. In any case <literal>JOIN</literal> binds more
tightly than the commas separating <literal>FROM</literal>-list items.
</para>
<para><literal>CROSS JOIN</literal> and <literal>INNER JOIN</literal>
produce a simple Cartesian product, the same result as you get from
listing the two tables at the top level of <literal>FROM</literal>,
but restricted by the join condition (if any).
<literal>CROSS JOIN</literal> is equivalent to <literal>INNER JOIN ON
(TRUE)</literal>, that is, no rows are removed by qualification.
These join types are just a notational convenience, since they
do nothing you couldn't do with plain <literal>FROM</literal> and
<literal>WHERE</literal>.
All the <literal>JOIN</literal> options are just a notational
convenience, since they do nothing you couldn't do with plain
<literal>FROM</literal> and <literal>WHERE</literal>.
</para>
<para><literal>LEFT OUTER JOIN</literal> returns all rows in the qualified
@ -714,6 +704,19 @@ TABLE [ ONLY ] <replaceable class="parameter">table_name</replaceable> [ * ]
</listitem>
</varlistentry>
<varlistentry>
<term><literal>CROSS JOIN</literal></term>
<listitem>
<para>
<literal>CROSS JOIN</literal> is equivalent to <literal>INNER JOIN ON
(TRUE)</literal>, that is, no rows are removed by qualification.
They produce a simple Cartesian product, the same result as you get from
listing the two tables at the top level of <literal>FROM</literal>,
but restricted by the join condition (if any).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>LATERAL</literal></term>
<listitem>
@ -1754,8 +1757,7 @@ SELECT * FROM <replaceable class="parameter">name</replaceable>
<programlisting>
SELECT f.title, f.did, d.name, f.date_prod, f.kind
FROM distributors d, films f
WHERE f.did = d.did
FROM distributors d JOIN films f USING (did);
title | did | name | date_prod | kind
-------------------+-----+--------------+------------+----------