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Add some basic support for window frame clauses to the window-functions

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patch.  This includes the ability to force the frame to cover the whole
partition, and the ability to make the frame end exactly on the current row
rather than its last ORDER BY peer.  Supporting any more of the full SQL
frame-clause syntax will require nontrivial hacking on the window aggregate
code, so it'll have to wait for 8.5 or beyond.
This commit is contained in:
Tom Lane
2008-12-31 00:08:39 +00:00
parent 0fb9be7acf
commit 8e8854daa2
24 changed files with 757 additions and 307 deletions
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60
doc/src/sgml/ref/select.sgml
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@@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/ref/select.sgml,v 1.114 2008/12/29 18:23:53 tgl Exp $
$PostgreSQL: pgsql/doc/src/sgml/ref/select.sgml,v 1.115 2008/12/31 00:08:35 tgl Exp $
PostgreSQL documentation
-->
@@ -583,7 +583,21 @@ WINDOW <replaceable class="parameter">window_name</replaceable> AS ( <replaceabl
[ <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 } ] [, ...] ]
[ <replaceable class="parameter">framing_clause</replaceable> ]
</synopsis>
</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.
The framing clause is never copied from the existing window.
</para>
<para>
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
@@ -597,12 +611,29 @@ WINDOW <replaceable class="parameter">window_name</replaceable> AS ( <replaceabl
</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.
The optional <replaceable class="parameter">framing_clause</> defines
the <firstterm>window frame</> for window functions that depend on the
frame (not all do). It can be one of
<synopsis>
RANGE UNBOUNDED PRECEDING
RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
RANGE BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING
ROWS UNBOUNDED PRECEDING
ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING
</synopsis>
The first two are equivalent and are also the default: they set the
frame to be all rows from the partition start up through the current row's
last peer in the <literal>ORDER BY</> ordering (which means all rows if
there is no <literal>ORDER BY</>). The options
<literal>RANGE BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING</> and
<literal>ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING</>
are also equivalent: they always select all rows in the partition.
Lastly, <literal>ROWS UNBOUNDED PRECEDING</> or its verbose equivalent
<literal>ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW</> select
all rows up through the current row (regardless of duplicates).
Beware that this option can produce implementation-dependent results
if the <literal>ORDER BY</> ordering does not order the rows uniquely.
</para>
<para>
@@ -623,8 +654,9 @@ WINDOW <replaceable class="parameter">window_name</replaceable> AS ( <replaceabl
<para>
Window functions are described in detail in
<xref linkend="tutorial-window"> and
<xref linkend="syntax-window-functions">.
<xref linkend="tutorial-window">,
<xref linkend="syntax-window-functions">, and
<xref linkend="queries-window">.
</para>
</refsect2>
@@ -1453,12 +1485,10 @@ SELECT distributors.* WHERE distributors.name = 'Westward';
<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>RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW</>.
The SQL standard provides additional options for the window
<replaceable class="parameter">framing_clause</>.
<productname>PostgreSQL</productname> currently supports only the
options listed above.
</para>
</refsect2>