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Add GROUP BY ALL.

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GROUP BY ALL is a form of GROUP BY that adds any TargetExpr that does
not contain an aggregate or window function into the groupClause of
the query, making it exactly equivalent to specifying those same
expressions in an explicit GROUP BY list.

This feature is useful for certain kinds of data exploration.  It's
already present in some other DBMSes, and the SQL committee recently
accepted it into the standard, so we can be reasonably confident in
the syntax being stable.  We do have to invent part of the semantics,
as the standard doesn't allow for expressions in GROUP BY, so they
haven't specified what to do with window functions.  We assume that
those should be treated like aggregates, i.e., left out of the
constructed GROUP BY list.

In passing, wordsmith some existing documentation about GROUP BY,
and update some neglected synopsis entries in select_into.sgml.

Author: David Christensen <david@pgguru.net>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/CAHM0NXjz0kDwtzoe-fnHAqPB1qA8_VJN0XAmCgUZ+iPnvP5LbA@mail.gmail.com
This commit is contained in:
Tom Lane
2025-09-29 16:55:17 -04:00
parent b91067c899
commit ef38a4d975
12 changed files with 312 additions and 15 deletions
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30
doc/src/sgml/queries.sgml
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@@ -1145,10 +1145,36 @@ SELECT product_id, p.name, (sum(s.units) * p.price) AS sales
<para>
In strict SQL, <literal>GROUP BY</literal> can only group by columns of
the source table but <productname>PostgreSQL</productname> extends
the source table, but <productname>PostgreSQL</productname> extends
this to also allow <literal>GROUP BY</literal> to group by columns in the
select list. Grouping by value expressions instead of simple
column names is also allowed.
column names is also allowed (but <literal>GROUP BY</literal>
expressions cannot contain aggregate functions or window functions).
</para>
<para>
PostgreSQL also supports the syntax <literal>GROUP BY ALL</literal>,
which is equivalent to explicitly writing all select-list entries that
do not contain either an aggregate function or a window function.
This can greatly simplify ad-hoc exploration of data.
As an example, these queries are equivalent:
<screen>
<prompt>=&gt;</prompt> <userinput>SELECT a, b, a + b, sum(c) FROM test1 GROUP BY ALL;</userinput>
a | b | ?column? | sum
---+---+----------+----
1 | 4 | 5 | 9
2 | 5 | 7 | 12
3 | 6 | 9 | 15
(3 rows)
<prompt>=&gt;</prompt> <userinput>SELECT a, b, a + b, sum(c) FROM test1 GROUP BY a, b, a + b;</userinput>
a | b | ?column? | sum
---+---+----------+----
1 | 4 | 5 | 9
2 | 5 | 7 | 12
3 | 6 | 9 | 15
(3 rows)
</screen>
</para>
<indexterm>

22
doc/src/sgml/ref/select.sgml
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@@ -37,7 +37,7 @@ SELECT [ ALL | DISTINCT [ ON ( <replaceable class="parameter">expression</replac
[ { * | <replaceable class="parameter">expression</replaceable> [ [ AS ] <replaceable class="parameter">output_name</replaceable> ] } [, ...] ]
[ FROM <replaceable class="parameter">from_item</replaceable> [, ...] ]
[ WHERE <replaceable class="parameter">condition</replaceable> ]
[ GROUP BY [ ALL | DISTINCT ] <replaceable class="parameter">grouping_element</replaceable> [, ...] ]
[ GROUP BY { ALL | [ ALL | DISTINCT ] <replaceable class="parameter">grouping_element</replaceable> [, ...] } ]
[ HAVING <replaceable class="parameter">condition</replaceable> ]
[ WINDOW <replaceable class="parameter">window_name</replaceable> AS ( <replaceable class="parameter">window_definition</replaceable> ) [, ...] ]
[ { UNION | INTERSECT | EXCEPT } [ ALL | DISTINCT ] <replaceable class="parameter">select</replaceable> ]
@@ -796,7 +796,7 @@ WHERE <replaceable class="parameter">condition</replaceable>
<para>
The optional <literal>GROUP BY</literal> clause has the general form
<synopsis>
GROUP BY [ ALL | DISTINCT ] <replaceable class="parameter">grouping_element</replaceable> [, ...]
GROUP BY { ALL | [ ALL | DISTINCT ] <replaceable class="parameter">grouping_element</replaceable> [, ...] }
</synopsis>
</para>
@@ -808,21 +808,31 @@ GROUP BY [ ALL | DISTINCT ] <replaceable class="parameter">grouping_element</rep
<replaceable class="parameter">grouping_element</replaceable>
can be an input column name, or the name or ordinal number of an
output column (<command>SELECT</command> list item), or an arbitrary
expression formed from input-column values. In case of ambiguity,
expression formed from input-column values; however, it cannot contain
an aggregate function or a window function. In case of ambiguity,
a <literal>GROUP BY</literal> name will be interpreted as an
input-column name rather than an output column name.
</para>
<para>
The form <literal>GROUP BY ALL</literal> with no explicit
<replaceable class="parameter">grouping_elements</replaceable>
provided is equivalent to writing <literal>GROUP BY</literal> with the
numbers of all <command>SELECT</command> output columns that do not
contain either an aggregate function or a window function.
</para>
<para>
If any of <literal>GROUPING SETS</literal>, <literal>ROLLUP</literal> or
<literal>CUBE</literal> are present as grouping elements, then the
<literal>GROUP BY</literal> clause as a whole defines some number of
independent <replaceable>grouping sets</replaceable>. The effect of this is
equivalent to constructing a <literal>UNION ALL</literal> between
subqueries with the individual grouping sets as their
subqueries having the individual grouping sets as their
<literal>GROUP BY</literal> clauses. The optional <literal>DISTINCT</literal>
clause removes duplicate sets before processing; it does <emphasis>not</emphasis>
transform the <literal>UNION ALL</literal> into a <literal>UNION DISTINCT</literal>.
key word removes duplicate grouping sets before processing; it does <emphasis>not</emphasis>
transform the implied <literal>UNION ALL</literal> into
a <literal>UNION DISTINCT</literal>.
For further details on the handling
of grouping sets see <xref linkend="queries-grouping-sets"/>.
</para>

6
doc/src/sgml/ref/select_into.sgml
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@@ -27,15 +27,15 @@ SELECT [ ALL | DISTINCT [ ON ( <replaceable class="parameter">expression</replac
INTO [ TEMPORARY | TEMP | UNLOGGED ] [ TABLE ] <replaceable class="parameter">new_table</replaceable>
[ FROM <replaceable class="parameter">from_item</replaceable> [, ...] ]
[ WHERE <replaceable class="parameter">condition</replaceable> ]
[ GROUP BY <replaceable class="parameter">expression</replaceable> [, ...] ]
[ GROUP BY { ALL | [ ALL | DISTINCT ] <replaceable class="parameter">grouping_element</replaceable> [, ...] } ]
[ HAVING <replaceable class="parameter">condition</replaceable> ]
[ WINDOW <replaceable class="parameter">window_name</replaceable> AS ( <replaceable class="parameter">window_definition</replaceable> ) [, ...] ]
[ { UNION | INTERSECT | EXCEPT } [ ALL | DISTINCT ] <replaceable class="parameter">select</replaceable> ]
[ ORDER BY <replaceable class="parameter">expression</replaceable> [ ASC | DESC | USING <replaceable class="parameter">operator</replaceable> ] [ NULLS { FIRST | LAST } ] [, ...] ]
[ LIMIT { <replaceable class="parameter">count</replaceable> | ALL } ]
[ OFFSET <replaceable class="parameter">start</replaceable> [ ROW | ROWS ] ]
[ FETCH { FIRST | NEXT } [ <replaceable class="parameter">count</replaceable> ] { ROW | ROWS } ONLY ]
[ FOR { UPDATE | SHARE } [ OF <replaceable class="parameter">table_name</replaceable> [, ...] ] [ NOWAIT ] [...] ]
[ FETCH { FIRST | NEXT } [ <replaceable class="parameter">count</replaceable> ] { ROW | ROWS } { ONLY | WITH TIES } ]
[ FOR { UPDATE | NO KEY UPDATE | SHARE | KEY SHARE } [ OF <replaceable class="parameter">from_reference</replaceable> [, ...] ] [ NOWAIT | SKIP LOCKED ] [...] ]
</synopsis>
</refsynopsisdiv>