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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/syntax.sgml
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@@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/syntax.sgml,v 1.127 2008/12/28 18:53:54 tgl Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/syntax.sgml,v 1.128 2008/12/31 00:08:35 tgl Exp $ -->
<chapter id="sql-syntax">
<title>SQL Syntax</title>
@@ -1591,6 +1591,17 @@ sqrt(2)
[ <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 } ] [, ...] ]
[ <replaceable class="parameter">framing_clause</replaceable> ]
</synopsis>
and the optional <replaceable class="parameter">framing_clause</replaceable>
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>
Here, <replaceable>expression</replaceable> represents any value
@@ -1603,19 +1614,33 @@ sqrt(2)
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</>.
optionally override its ordering clause and/or framing clause.
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 default framing option is <literal>RANGE UNBOUNDED PRECEDING</>,
which is the same as <literal>RANGE BETWEEN UNBOUNDED PRECEDING AND
CURRENT ROW</>; it selects rows 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>
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>