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Allow an alias to be attached to a JOIN ... USING

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This allows something like

    SELECT ... FROM t1 JOIN t2 USING (a, b, c) AS x

where x has the columns a, b, c and unlike a regular alias it does not
hide the range variables of the tables being joined t1 and t2.

Per SQL:2016 feature F404 "Range variable for common column names".

Reviewed-by: Vik Fearing <vik.fearing@2ndquadrant.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://www.postgresql.org/message-id/flat/454638cf-d563-ab76-a585-2564428062af@2ndquadrant.com
This commit is contained in:
Peter Eisentraut
2021-03-31 17:09:24 +02:00
parent 27e1f14563
commit 055fee7eb4
22 changed files with 315 additions and 29 deletions
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16
doc/src/sgml/ref/select.sgml
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@ -59,7 +59,7 @@ 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> [, ...] ) ]
<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> ] ]
<phrase>and <replaceable class="parameter">grouping_element</replaceable> can be one of:</phrase>
@ -676,7 +676,7 @@ TABLE [ ONLY ] <replaceable class="parameter">table_name</replaceable> [ * ]
</varlistentry>
<varlistentry>
<term><literal>USING ( <replaceable class="parameter">join_column</replaceable> [, ...] )</literal></term>
<term><literal>USING ( <replaceable class="parameter">join_column</replaceable> [, ...] ) [ AS <replaceable class="parameter">join_using_alias</replaceable> ]</literal></term>
<listitem>
<para>
A clause of the form <literal>USING ( a, b, ... )</literal> is
@ -686,6 +686,18 @@ TABLE [ ONLY ] <replaceable class="parameter">table_name</replaceable> [ * ]
equivalent columns will be included in the join output, not
both.
</para>
<para>
If a <replaceable class="parameter">join_using_alias</replaceable>
name is specified, it provides a table alias for the join columns.
Only the join columns listed in the <literal>USING</literal> clause
are addressable by this name. Unlike a regular <replaceable
class="parameter">alias</replaceable>, this does not hide the names of
the joined tables from the rest of the query. Also unlike a regular
<replaceable class="parameter">alias</replaceable>, you cannot write a
column alias list &mdash; the output names of the join columns are the
same as they appear in the <literal>USING</literal> list.
</para>
</listitem>
</varlistentry>