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Aggregate functions now support multiple input arguments. I also took

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the opportunity to treat COUNT(*) as a zero-argument aggregate instead
of the old hack that equated it to COUNT(1); this is materially cleaner
(no more weird ANYOID cases) and ought to be at least a tiny bit faster.
Original patch by Sergey Koposov; review, documentation, simple regression
tests, pg_dump and psql support by moi.
This commit is contained in:
Tom Lane
2006-07-27 19:52:07 +00:00
parent c2d1138351
commit 108fe47301
39 changed files with 702 additions and 484 deletions
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30
doc/src/sgml/syntax.sgml
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@@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/syntax.sgml,v 1.107 2006/06/26 17:24:40 tgl Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/syntax.sgml,v 1.108 2006/07/27 19:52:04 tgl Exp $ -->
<chapter id="sql-syntax">
<title>SQL Syntax</title>
@@ -673,8 +673,9 @@ CAST ( '<replaceable>string</replaceable>' AS <replaceable>type</replaceable> )
<para>
The asterisk (<literal>*</literal>) is used in some contexts to denote
all the fields of a table row or composite value. It also
has a special meaning when used as the argument of the
<function>COUNT</function> aggregate function.
has a special meaning when used as the argument of an
aggregate function, namely that the aggregate does not require
any explicit parameter.
</para>
</listitem>
@@ -1269,9 +1270,9 @@ sqrt(2)
syntax of an aggregate expression is one of the following:
<synopsis>
<replaceable>aggregate_name</replaceable> (<replaceable>expression</replaceable>)
<replaceable>aggregate_name</replaceable> (ALL <replaceable>expression</replaceable>)
<replaceable>aggregate_name</replaceable> (DISTINCT <replaceable>expression</replaceable>)
<replaceable>aggregate_name</replaceable> (<replaceable>expression</replaceable> [ , ... ] )
<replaceable>aggregate_name</replaceable> (ALL <replaceable>expression</replaceable> [ , ... ] )
<replaceable>aggregate_name</replaceable> (DISTINCT <replaceable>expression</replaceable> [ , ... ] )
<replaceable>aggregate_name</replaceable> ( * )
</synopsis>
@@ -1284,16 +1285,16 @@ sqrt(2)
<para>
The first form of aggregate expression invokes the aggregate
across all input rows for which the given expression yields a
non-null value. (Actually, it is up to the aggregate function
across all input rows for which the given expression(s) yield
non-null values. (Actually, it is up to the aggregate function
whether to ignore null values or not &mdash; but all the standard ones do.)
The second form is the same as the first, since
<literal>ALL</literal> is the default. The third form invokes the
aggregate for all distinct non-null values of the expression found
aggregate for all distinct non-null values of the expressions found
in the input rows. The last form invokes the aggregate once for
each input row regardless of null or non-null values; since no
particular input value is specified, it is generally only useful
for the <function>count()</function> aggregate function.
for the <function>count(*)</function> aggregate function.
</para>
<para>
@@ -1323,7 +1324,7 @@ sqrt(2)
<xref linkend="sql-syntax-scalar-subqueries"> and
<xref linkend="functions-subquery">), the aggregate is normally
evaluated over the rows of the subquery. But an exception occurs
if the aggregate's argument contains only outer-level variables:
if the aggregate's arguments contain only outer-level variables:
the aggregate then belongs to the nearest such outer level, and is
evaluated over the rows of that query. The aggregate expression
as a whole is then an outer reference for the subquery it appears in,
@@ -1332,6 +1333,13 @@ sqrt(2)
appearing only in the result list or <literal>HAVING</> clause
applies with respect to the query level that the aggregate belongs to.
</para>
<note>
<para>
<productname>PostgreSQL</productname> currently does not support
<literal>DISTINCT</> with more than one input expression.
</para>
</note>
</sect2>
<sect2 id="sql-syntax-type-casts">