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Diffstat (limited to 'doc/src/sgml/advanced.sgml')
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1 files changed, 20 insertions, 13 deletions
diff --git a/doc/src/sgml/advanced.sgml b/doc/src/sgml/advanced.sgml index ce8ef535db..42d923b00d 100644 --- a/doc/src/sgml/advanced.sgml +++ b/doc/src/sgml/advanced.sgml @@ -1,4 +1,4 @@ -<!-- $PostgreSQL: pgsql/doc/src/sgml/advanced.sgml,v 1.55 2008/12/28 18:53:53 tgl Exp $ --> +<!-- $PostgreSQL: pgsql/doc/src/sgml/advanced.sgml,v 1.56 2008/12/31 00:08:32 tgl Exp $ --> <chapter id="tutorial-advanced"> <title>Advanced Features</title> @@ -429,27 +429,27 @@ SELECT depname, empno, salary, rank() OVER (PARTITION BY depname ORDER BY salary <para> We already saw that <literal>ORDER BY</> can be omitted if the ordering of rows is not important. It is also possible to omit <literal>PARTITION - BY</>, in which case the window function is computed over all rows of the - virtual table; that is, there is one partition containing all the rows. + BY</>, in which case there is just one partition containing all the rows. </para> <para> There is another important concept associated with window functions: for each row, there is a set of rows within its partition called its - <firstterm>window frame</>. When <literal>ORDER BY</> is omitted the - frame is always the same as the partition. If <literal>ORDER BY</> is - supplied, the frame consists of all rows from the start of the partition - up to the current row, plus any following rows that are equal to the - current row according to the <literal>ORDER BY</> clause. + <firstterm>window frame</>. Many (but not all) window functions act only + on the rows of the window frame, rather than of the whole partition. + By default, if <literal>ORDER BY</> is supplied then the frame consists of + all rows from the start of the partition up through the current row, plus + any following rows that are equal to the current row according to the + <literal>ORDER BY</> clause. When <literal>ORDER BY</> is omitted the + default frame consists of all rows in the partition. <footnote> <para> - The SQL standard includes options to define the window frame in - other ways, but this definition is the only one currently supported - by <productname>PostgreSQL</productname>. + There are options to define the window frame in other ways, but + this tutorial does not cover them. See + <xref linkend="syntax-window-functions"> for details. </para> </footnote> - Many window functions act only on the rows of the window frame, rather - than of the whole partition. Here is an example using <function>sum</>: + Here is an example using <function>sum</>: </para> <programlisting> @@ -550,6 +550,13 @@ SELECT sum(salary) OVER w, avg(salary) OVER w WINDOW w AS (PARTITION BY depname ORDER BY salary DESC); </programlisting> </para> + + <para> + More details about window functions can be found in + <xref linkend="syntax-window-functions">, + <xref linkend="queries-window">, and the + <xref linkend="sql-select" endterm="sql-select-title"> reference page. + </para> </sect1> |