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Support window functions a la SQL:2008.

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Hitoshi Harada, with some kibitzing from Heikki and Tom.
This commit is contained in:
Tom Lane
2008-12-28 18:54:01 +00:00
parent 38e9348282
commit 95b07bc7f5
92 changed files with 6720 additions and 321 deletions
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97
doc/src/sgml/syntax.sgml
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@@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/syntax.sgml,v 1.126 2008/12/09 20:52:03 tgl Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/syntax.sgml,v 1.127 2008/12/28 18:53:54 tgl Exp $ -->
<chapter id="sql-syntax">
<title>SQL Syntax</title>
@@ -1201,6 +1201,12 @@ SELECT 3 OPERATOR(pg_catalog.+) 4;
</para>
</listitem>
<listitem>
<para>
A window function call.
</para>
</listitem>
<listitem>
<para>
A type cast.
@@ -1445,7 +1451,7 @@ $1.somecolumn
enclosed in parentheses:
<synopsis>
<replaceable>function</replaceable> (<optional><replaceable>expression</replaceable> <optional>, <replaceable>expression</replaceable> ... </optional></optional> )
<replaceable>function_name</replaceable> (<optional><replaceable>expression</replaceable> <optional>, <replaceable>expression</replaceable> ... </optional></optional> )
</synopsis>
</para>
@@ -1480,7 +1486,7 @@ sqrt(2)
<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> (DISTINCT <replaceable>expression</replaceable>)
<replaceable>aggregate_name</replaceable> ( * )
</synopsis>
@@ -1488,7 +1494,7 @@ sqrt(2)
defined aggregate (possibly qualified with a schema name), and
<replaceable>expression</replaceable> is
any value expression that does not itself contain an aggregate
expression.
expression or a window function call.
</para>
<para>
@@ -1550,6 +1556,89 @@ sqrt(2)
</note>
</sect2>
<sect2 id="syntax-window-functions">
<title>Window Function Calls</title>
<indexterm zone="syntax-window-functions">
<primary>window function</primary>
<secondary>invocation</secondary>
</indexterm>
<indexterm zone="syntax-window-functions">
<primary>OVER clause</primary>
</indexterm>
<para>
A <firstterm>window function call</firstterm> represents the application
of an aggregate-like function over some portion of the rows selected
by a query. Unlike regular aggregate function calls, this is not tied
to grouping of the selected rows into a single output row &mdash; each
row remains separate in the query output. However the window function
is able to scan all the rows that would be part of the current row's
group according to the grouping specification (<literal>PARTITION BY</>
list) of the window function call.
The syntax of a window function call is one of the following:
<synopsis>
<replaceable>function_name</replaceable> (<optional><replaceable>expression</replaceable> <optional>, <replaceable>expression</replaceable> ... </optional></optional>) OVER ( <replaceable class="parameter">window_definition</replaceable> )
<replaceable>function_name</replaceable> (<optional><replaceable>expression</replaceable> <optional>, <replaceable>expression</replaceable> ... </optional></optional>) OVER <replaceable>window_name</replaceable>
<replaceable>function_name</replaceable> ( * ) OVER ( <replaceable class="parameter">window_definition</replaceable> )
<replaceable>function_name</replaceable> ( * ) OVER <replaceable>window_name</replaceable>
</synopsis>
where <replaceable class="parameter">window_definition</replaceable>
has the syntax
<synopsis>
[ <replaceable class="parameter">window_name</replaceable> ]
[ PARTITION BY <replaceable class="parameter">expression</replaceable> [, ...] ]
[ ORDER BY <replaceable class="parameter">expression</replaceable> [ ASC | DESC | USING <replaceable class="parameter">operator</replaceable> ] [ NULLS { FIRST | LAST } ] [, ...] ]
</synopsis>
Here, <replaceable>expression</replaceable> represents any value
expression that does not itself contain window function calls.
The <literal>PARTITION BY</> and <literal>ORDER BY</> lists have
essentially the same syntax and semantics as <literal>GROUP BY</>
and <literal>ORDER BY</> clauses of the whole query.
<replaceable>window_name</replaceable> is a reference to a named window
specification defined in the query's <literal>WINDOW</literal> clause.
Named window specifications are usually referenced with just
<literal>OVER</> <replaceable>window_name</replaceable>, but it is
also possible to write a window name inside the parentheses and then
optionally override its ordering clause with <literal>ORDER BY</>.
This latter syntax follows the same rules as modifying an existing
window name within the <literal>WINDOW</literal> clause; see the
<xref linkend="sql-select" endterm="sql-select-title"> reference
page for details.
</para>
<para>
The built-in window functions are described in <xref
linkend="functions-window-table">. Also, any built-in or
user-defined aggregate function can be used as a window function.
Currently, there is no provision for user-defined window functions
other than aggregates.
</para>
<para>
The syntaxes using <literal>*</> are used for calling parameter-less
aggregate functions as window functions, for example
<literal>count(*) OVER (PARTITION BY x ORDER BY y)</>.
<literal>*</> is customarily not used for non-aggregate window functions.
Aggregate window functions, unlike normal aggregate functions, do not
allow <literal>DISTINCT</> to be used within the function argument list.
</para>
<para>
Window function calls are permitted only in the <literal>SELECT</literal>
list and the <literal>ORDER BY</> clause of the query.
</para>
<para>
More information about window functions can be found in
<xref linkend="tutorial-window"> and
<xref linkend="queries-window">.
</para>
</sect2>
<sect2 id="sql-syntax-type-casts">
<title>Type Casts</title>