8000 Copy-editing for recent window-functions documentation rewrite. · postgrespro/postgres@1822684 · GitHub
[go: up one dir, main page]
Skip to content

Commit 1822684

Browse files
tglsfdctglsfdc
committed
Copy-editing for recent window-functions documentation rewrite.
Fix grammar, put back some removed information, rearrange for clarity.
1 parent 470d0b9 commit 1822684

File tree

1 file changed

+45
-23
lines changed

1 file changed

+45
-23
lines changed

‎doc/src/sgml/syntax.sgml

Lines changed: 45 additions & 23 deletions
Original file line numberDiff line numberDiff line change
@@ -1742,13 +1742,6 @@ UNBOUNDED FOLLOWING
17421742
<para>
17431743
Here, <replaceable>expression</replaceable> represents any value
17441744
expression that does not itself contain window function calls.
1745-
<literal>PARTITION BY</> behaves like a <literal>GROUP
1746-
BY</> clause by grouping rows into partitions, except its
1747-
expressions are always just expressions and cannot be output-column
1748-
names or numbers. <literal>ORDER BY</> behaves similar to a
1749-
query-level <literal>ORDER BY</> clause, except it controls the
1750-
order rows are supplied to the aggregate function within the window
1751-
frame, and with the same expression restrictions.
17521745
</para>
17531746

17541747
<para>
@@ -1766,18 +1759,49 @@ UNBOUNDED FOLLOWING
17661759
</para>
17671760

17681761
<para>
1769-
In <literal>RANGE</> mode, <literal>CURRENT ROW</> starts with
1770-
the current row's first peer that <literal>ORDER BY</>
1771-
considers equivalent, and ends with its last equivalent peer. In
1772-
<literal>ROWS</> mode, <literal>CURRENT ROW</> simply starts and ends
1773-
with the current row.
1762+
The <literal>PARTITION BY</> option groups the rows of the query into
1763+
<firstterm>partitions</>, which are processed separately by the window
1764+
function. <literal>PARTITION BY</> works similarly to a query-level
1765+
<literal>GROUP BY</> clause, except that its expressions are always just
1766+
expressions and cannot be output-column names or numbers.
1767+
Without <literal>PARTITION BY</>, all rows produced by the query are
1768+
treated as a single partition.
1769+
The <literal>ORDER BY</> option determines the order in which the rows
1770+
of a partition are processed by the window function. It works similarly
1771+
to a query-level <literal>ORDER BY</> clause, but likewise cannot use
1772+
output-column names or numbers. Without <literal>ORDER BY</>, rows are
1773+
processed in an unspecified order.
1774+
</para>
1775+
1776+
<para>
1777+
The <replaceable class="parameter">frame_clause</replaceable> specifies
1778+
the set of rows constituting the <firstterm>window frame</>, which is a
1779+
subset of the current partition, for those window functions that act on
1780+
the frame instead of the whole partition. The frame can be specified in
1781+
either <literal>RANGE</> or <literal>ROWS</> mode; in either case, it
1782+
runs from the <replaceable>frame_start</> to the
1783+
<replaceable>frame_end</>. If <replaceable>frame_end</> is omitted,
1784+
it defaults to <literal>CURRENT ROW</>.
1785+
</para>
1786+
1787+
<para>
1788+
A <replaceable>frame_start</> of <literal>UNBOUNDED PRECEDING</> means
1789+
that the frame starts with the first row of the partition, and similarly
1790+
a <replaceable>frame_end</> of <literal>UNBOUNDED FOLLOWING</> means
1791+
that the frame ends with the last row of the partition.
1792+
</para>
1793+
1794+
<para>
1795+
In <literal>RANGE</> mode, a <replaceable>frame_start</> of
1796+
<literal>CURRENT ROW</> means the frame starts with the current row's
1797+
first <firstterm>peer</> row (a row that <literal>ORDER BY</> considers
1798+
equivalent to the current row), while a <replaceable>frame_end</> of
1799+
<literal>CURRENT ROW</> means the frame ends with the last equivalent
1800+
peer. In <literal>ROWS</> mode, <literal>CURRENT ROW</> simply means
1801+
the current row.
17741802
</para>
17751803

17761804
<para>
1777-
<literal>UNBOUNDED PRECEDING</> means that the frame
1778-
starts with the first row of the partition, and similarly
1779-
<literal>UNBOUNDED FOLLOWING</> means that the frame ends with the last
1780-
row of the partition.
17811805
The <replaceable>value</> <literal>PRECEDING</> and
17821806
<replaceable>value</> <literal>FOLLOWING</> cases are currently only
17831807
allowed in <literal>ROWS</> mode. They indicate that the frame starts
@@ -1789,15 +1813,13 @@ UNBOUNDED FOLLOWING
17891813
</para>
17901814

17911815
<para>
1792-
The <replaceable class="parameter">frame_clause</replaceable> specifies
1793-
the set of rows constituting the <firstterm>window frame</>, for those
1794-
window functions that act on the frame instead of the whole partition.
17951816
The default framing option is <literal>RANGE UNBOUNDED PRECEDING</>,
17961817
which is the same as <literal>RANGE BETWEEN UNBOUNDED PRECEDING AND
1797-
CURRENT ROW</>. With < 7409 ;literal>ORDER BY</>, this sets the frame to
1798-
be all rows from partition start up through the current row's
1799-
last peer. Without <literal>ORDER BY</>, all partition rows are
1800-
included in the window frame.
1818+
CURRENT ROW</>. With <literal>ORDER BY</>, this sets the frame to be
1819+
all rows from the partition start up through the current row's last
1820+
peer. Without <literal>ORDER BY</>, all rows of the partition are
1821+
included in the window frame, since all rows become peers of the current
1822+
row.
18011823
</para>
18021824

18031825
<para>

0 commit comments

Comments
 (0)
0