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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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79
doc/src/sgml/ref/select.sgml
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@@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/ref/select.sgml,v 1.112 2008/12/01 09:38:08 petere Exp $
$PostgreSQL: pgsql/doc/src/sgml/ref/select.sgml,v 1.113 2008/12/28 18:53:54 tgl Exp $
PostgreSQL documentation
-->
@@ -39,6 +39,7 @@ SELECT [ ALL | DISTINCT [ ON ( <replaceable class="parameter">expression</replac
[ WHERE <replaceable class="parameter">condition</replaceable> ]
[ GROUP BY <replaceable class="parameter">expression</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 ] <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 } ]
@@ -566,6 +567,67 @@ HAVING <replaceable class="parameter">condition</replaceable>
</para>
</refsect2>
<refsect2 id="SQL-WINDOW">
<title id="sql-window-title"><literal>WINDOW</literal> Clause</title>
<para>
The optional <literal>WINDOW</literal> clause has the general form
<synopsis>
WINDOW <replaceable class="parameter">window_name</replaceable> AS ( <replaceable class="parameter">window_definition</replaceable> ) [, ...]
</synopsis>
where <replaceable class="parameter">window_name</replaceable> is
a name that can be referenced from subsequent window definitions or
<literal>OVER</> clauses, and
<replaceable class="parameter">window_definition</replaceable> is
<synopsis>
[ <replaceable class="parameter">existing_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>
The elements of the <literal>PARTITION BY</> list are interpreted in
the same fashion as elements of a
<xref linkend="sql-groupby" endterm="sql-groupby-title">, and
the elements of the <literal>ORDER BY</> list are interpreted in the
same fashion as elements of an
<xref linkend="sql-orderby" endterm="sql-orderby-title">.
The only difference is that these expressions can contain aggregate
function calls, which are not allowed in a regular <literal>GROUP BY</>
clause. They are allowed here because windowing occurs after grouping
and aggregation.
</para>
<para>
If an <replaceable class="parameter">existing_window_name</replaceable>
is specified it must refer to an earlier entry in the <literal>WINDOW</>
list; the new window copies its partitioning clause from that entry,
as well as its ordering clause if any. In this case the new window cannot
specify its own <literal>PARTITION BY</> clause, and it can specify
<literal>ORDER BY</> only if the copied window does not have one.
</para>
<para>
The purpose of a <literal>WINDOW</literal> clause is to specify the
behavior of <firstterm>window functions</> appearing in the query's
<xref linkend="sql-select-list" endterm="sql-select-list-title"> or
<xref linkend="sql-orderby" endterm="sql-orderby-title">. These functions
can reference the <literal>WINDOW</literal> clause entries by name
in their <literal>OVER</> clauses. A <literal>WINDOW</literal> clause
entry does not have to be referenced anywhere, however; if it is not
used in the query it is simply ignored. It is possible to use window
functions without any <literal>WINDOW</literal> clause at all, since
a window function call can specify its window definition directly in
its <literal>OVER</> clause. However, the <literal>WINDOW</literal>
clause saves typing when the same window definition is needed for more
than one window function.
</para>
<para>
Window functions are described in detail in
<xref linkend="tutorial-window"> and
<xref linkend="syntax-window-functions">.
</para>
</refsect2>
<refsect2 id="sql-select-list">
<title id="sql-select-list-title"><command>SELECT</command> List</title>
@@ -922,7 +984,7 @@ FETCH { FIRST | NEXT } [ <replaceable class="parameter">count</replaceable> ] {
constants for the offset or fetch count, parentheses will be
necessary in most cases. If the fetch count is omitted, it
defaults to 1.
</para>
</para>
<para>
When using <literal>LIMIT</>, it is a good idea to use an
@@ -1387,6 +1449,19 @@ SELECT distributors.* WHERE distributors.name = 'Westward';
</para>
</refsect2>
<refsect2>
<title><literal>WINDOW</literal> Clause Restrictions</title>
<para>
The SQL standard provides for an optional <quote>framing clause</>,
introduced by the key word <literal>RANGE</> or <literal>ROWS</>,
in window definitions. <productname>PostgreSQL</productname> does
not yet implement framing clauses, and always follows the
default framing behavior, which is equivalent to the framing clause
<literal>ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW</>.
</para>
</refsect2>
<refsect2>
<title><literal>LIMIT</literal> and <literal>OFFSET</literal></title>