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Extend the set of frame options supported for window functions.

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This patch allows the frame to start from CURRENT ROW (in either RANGE or
ROWS mode), and it also adds support for ROWS n PRECEDING and ROWS n FOLLOWING
start and end points.  (RANGE value PRECEDING/FOLLOWING isn't there yet ---
the grammar works, but that's all.)

Hitoshi Harada, reviewed by Pavel Stehule
This commit is contained in:
Tom Lane
2010-02-12 17:33:21 +00:00
parent a5348fafd1
commit ec4be2ee68
28 changed files with 1237 additions and 254 deletions
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22
doc/src/sgml/func.sgml
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@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.501 2010/02/07 20:48:09 tgl Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.502 2010/02/12 17:33:19 tgl Exp $ -->
<chapter id="functions">
<title>Functions and Operators</title>
@ -10559,21 +10559,23 @@ SELECT xmlagg(x) FROM (SELECT x FROM test ORDER BY y DESC) AS tab;
<function>nth_value</> consider only the rows within the <quote>window
frame</>, which by default contains the rows from the start of the
partition through the last peer of the current row. This is
likely to give unhelpful results for <function>nth_value</> and
particularly <function>last_value</>. You can redefine the frame as
being the whole partition by adding <literal>ROWS BETWEEN UNBOUNDED
PRECEDING AND UNBOUNDED FOLLOWING</> to the <literal>OVER</> clause.
See <xref linkend="syntax-window-functions"> for more information.
likely to give unhelpful results for <function>last_value</> and
sometimes also <function>nth_value</>. You can redefine the frame by
adding a suitable frame specification (<literal>RANGE</> or
<literal>ROWS</>) to the <literal>OVER</> clause.
See <xref linkend="syntax-window-functions"> for more information
about frame specifications.
</para>
<para>
When an aggregate function is used as a window function, it aggregates
over the rows within the current row's window frame. To obtain
aggregation over the whole partition, omit <literal>ORDER BY</> or use
<literal>ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING</>.
over the rows within the current row's window frame.
An aggregate used with <literal>ORDER BY</> and the default window frame
definition produces a <quote>running sum</> type of behavior, which may or
may not be what's wanted.
may not be what's wanted. To obtain
aggregation over the whole partition, omit <literal>ORDER BY</> or use
<literal>ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING</>.
Other frame specifications can be used to obtain other effects.
</para>
<note>