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Clarify documentation about "peer" rows in window functions

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Peer rows are matching rows when ORDER BY is specified.

Report by arnaud.mouronval@gmail.com, David G Johnston
This commit is contained in:
Bruce Momjian 2014-09-05 18:59:41 -04:00
parent a9c22d1480
commit 1f4d1074c5
3 changed files with 8 additions and 6 deletions
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3
doc/src/sgml/func.sgml
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@ -13050,7 +13050,8 @@ SELECT xmlagg(x) FROM (SELECT x FROM test ORDER BY y DESC) AS tab;
<firstterm>Window functions</firstterm> provide the ability to perform
calculations across sets of rows that are related to the current query
row. See <xref linkend="tutorial-window"> for an introduction to this
feature.
feature, and <xref linkend="syntax-window-functions"> for syntax
details.
</para>
<para>

7
doc/src/sgml/ref/select.sgml
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@ -792,8 +792,9 @@ UNBOUNDED FOLLOWING
The default framing option is <literal>RANGE UNBOUNDED PRECEDING</>,
which is the same as <literal>RANGE BETWEEN UNBOUNDED PRECEDING AND
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</>).
up through the current row's last peer (a row that <literal>ORDER
BY</> considers equivalent to the current row, or 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
@ -817,7 +818,7 @@ UNBOUNDED FOLLOWING
results if the <literal>ORDER BY</> ordering does not order the rows
uniquely. The <literal>RANGE</> options are designed to ensure that
rows that are peers in the <literal>ORDER BY</> ordering are treated
alike; any two peer rows will be both in or both not in the frame.
alike; all peer rows will be in the same frame.
</para>
<para>

4
doc/src/sgml/syntax.sgml
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@ -1877,7 +1877,7 @@ UNBOUNDED FOLLOWING
first <firstterm>peer</> row (a row that <literal>ORDER BY</> considers
equivalent to the current row), while a <replaceable>frame_end</> of
<literal>CURRENT ROW</> means the frame ends with the last equivalent
peer. In <literal>ROWS</> mode, <literal>CURRENT ROW</> simply means
<literal>ORDER BY</> peer. In <literal>ROWS</> mode, <literal>CURRENT ROW</> simply means
the current row.
</para>
@ -1897,7 +1897,7 @@ UNBOUNDED FOLLOWING
which is the same as <literal>RANGE BETWEEN UNBOUNDED PRECEDING AND
CURRENT ROW</>. With <literal>ORDER BY</>, this sets the frame to be
all rows from the partition start up through the current row's last
peer. Without <literal>ORDER BY</>, all rows of the partition are
<literal>ORDER BY</> peer. Without <literal>ORDER BY</>, all rows of the partition are
included in the window frame, since all rows become peers of the current
row.
</para>