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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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59
doc/src/sgml/syntax.sgml
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@@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/syntax.sgml,v 1.141 2010/02/04 00:19:28 tgl Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/syntax.sgml,v 1.142 2010/02/12 17:33:19 tgl Exp $ -->
<chapter id="sql-syntax">
<title>SQL Syntax</title>
@@ -1667,14 +1667,21 @@ SELECT array_agg(a ORDER BY b DESC) FROM table;
and the optional <replaceable class="parameter">frame_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
[ RANGE | ROWS ] <replaceable>frame_start</>
[ RANGE | ROWS ] BETWEEN <replaceable>frame_start</> AND <replaceable>frame_end</>
</synopsis>
where <replaceable>frame_start</> and <replaceable>frame_end</> can be
one of
<synopsis>
UNBOUNDED PRECEDING
<replaceable>value</replaceable> PRECEDING
CURRENT ROW
<replaceable>value</replaceable> FOLLOWING
UNBOUNDED FOLLOWING
</synopsis>
</para>
<para>
Here, <replaceable>expression</replaceable> represents any value
expression that does not itself contain window function calls.
The <literal>PARTITION BY</> and <literal>ORDER BY</> lists have
@@ -1699,19 +1706,35 @@ ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING
The <replaceable class="parameter">frame_clause</replaceable> specifies
the set of rows constituting the <firstterm>window frame</>, for those
window functions that act on the frame instead of the whole partition.
If <replaceable>frame_end</> is omitted it defaults to <literal>CURRENT
ROW</>. Restrictions are that
<replaceable>frame_start</> cannot be <literal>UNBOUNDED FOLLOWING</>,
<replaceable>frame_end</> cannot be <literal>UNBOUNDED PRECEDING</>,
and the <replaceable>frame_end</> choice cannot appear earlier in the
above list than the <replaceable>frame_start</> choice &mdash; for example
<literal>RANGE BETWEEN CURRENT ROW AND <replaceable>value</>
PRECEDING</literal> is not allowed.
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.
CURRENT ROW</>; it sets 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</>).
In general, <literal>UNBOUNDED PRECEDING</> means that the frame
starts with the first row of the partition, and similarly
<literal>UNBOUNDED FOLLOWING</> means that the frame ends with the last
row of the partition (regardless of <literal>RANGE</> or <literal>ROWS</>
mode). In <literal>ROWS</> mode, <literal>CURRENT ROW</>
means that the frame starts or ends with the current row; but in
<literal>RANGE</> mode it means that the frame starts or ends with
the current row's first or last peer in the <literal>ORDER BY</> ordering.
The <replaceable>value</> <literal>PRECEDING</> and
<replaceable>value</> <literal>FOLLOWING</> cases are currently only
allowed in <literal>ROWS</> mode. They indicate that the frame starts
or ends with the row that many rows before or after the current row.
<replaceable>value</replaceable> must be an integer expression not
containing any variables, aggregate functions, or window functions.
The value must not be null or negative; but it can be zero, which
selects the current row itself.
</para>
<para>