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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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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>