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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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33
doc/src/sgml/advanced.sgml
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@@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/advanced.sgml,v 1.55 2008/12/28 18:53:53 tgl Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/advanced.sgml,v 1.56 2008/12/31 00:08:32 tgl Exp $ -->
<chapter id="tutorial-advanced">
<title>Advanced Features</title>
@@ -429,27 +429,27 @@ SELECT depname, empno, salary, rank() OVER (PARTITION BY depname ORDER BY salary
<para>
We already saw that <literal>ORDER BY</> can be omitted if the ordering
of rows is not important. It is also possible to omit <literal>PARTITION
BY</>, in which case the window function is computed over all rows of the
virtual table; that is, there is one partition containing all the rows.
BY</>, in which case there is just one partition containing all the rows.
</para>
<para>
There is another important concept associated with window functions:
for each row, there is a set of rows within its partition called its
<firstterm>window frame</>. When <literal>ORDER BY</> is omitted the
frame is always the same as the partition. If <literal>ORDER BY</> is
supplied, the frame consists of all rows from the start of the partition
up to the current row, plus any following rows that are equal to the
current row according to the <literal>ORDER BY</> clause.
<firstterm>window frame</>. Many (but not all) window functions act only
on the rows of the window frame, rather than of the whole partition.
By default, if <literal>ORDER BY</> is supplied then the frame consists of
all rows from the start of the partition up through the current row, plus
any following rows that are equal to the current row according to the
<literal>ORDER BY</> clause. When <literal>ORDER BY</> is omitted the
default frame consists of all rows in the partition.
<footnote>
<para>
The SQL standard includes options to define the window frame in
other ways, but this definition is the only one currently supported
by <productname>PostgreSQL</productname>.
There are options to define the window frame in other ways, but
this tutorial does not cover them. See
<xref linkend="syntax-window-functions"> for details.
</para>
</footnote>
Many window functions act only on the rows of the window frame, rather
than of the whole partition. Here is an example using <function>sum</>:
Here is an example using <function>sum</>:
</para>
<programlisting>
@@ -550,6 +550,13 @@ SELECT sum(salary) OVER w, avg(salary) OVER w
WINDOW w AS (PARTITION BY depname ORDER BY salary DESC);
</programlisting>
</para>
<para>
More details about window functions can be found in
<xref linkend="syntax-window-functions">,
<xref linkend="queries-window">, and the
<xref linkend="sql-select" endterm="sql-select-title"> reference page.
</para>
</sect1>