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Marginal editorial improvements for array_agg patch documentation.

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This commit is contained in:
Tom Lane 2008-11-13 23:01:09 +00:00
parent 312d51798f
commit c23b6fa7b5
1 changed files with 11 additions and 11 deletions
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22
doc/src/sgml/func.sgml
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@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.458 2008/11/13 15:59:50 petere Exp $ --> <!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.459 2008/11/13 23:01:09 tgl Exp $ -->
<chapter id="functions"> <chapter id="functions">
<title>Functions and Operators</title> <title>Functions and Operators</title>
@ -8387,8 +8387,8 @@ SELECT xmlagg(x) FROM test;
</para> </para>
<para> <para>
The influence the order of the concatenation, something like the To determine the order of the concatenation, something like the
following approach to sort the input values can be used: following approach can be used:
<screen><![CDATA[ <screen><![CDATA[
SELECT xmlagg(x) FROM (SELECT * FROM test ORDER BY y DESC) AS tab; SELECT xmlagg(x) FROM (SELECT * FROM test ORDER BY y DESC) AS tab;
@ -9772,19 +9772,19 @@ SELECT count(*) FROM sometable;
and <function>xmlagg</function>, as well as similar user-defined and <function>xmlagg</function>, as well as similar user-defined
aggregate functions, produce meaningfully different result values aggregate functions, produce meaningfully different result values
depending on the order of the input values. In the current depending on the order of the input values. In the current
implementation, the order of the concatenation is in principle implementation, the order of the input is in principle unspecified.
undefined. Making the input values to be sorted in some other way Supplying the input values from a sorted subquery
will usually work, however. For example: will usually work, however. For example:
<screen><![CDATA[ <screen><![CDATA[
SELECT xmlagg(x) FROM (SELECT * FROM test ORDER BY y DESC) AS tab; SELECT xmlagg(x) FROM (SELECT x FROM test ORDER BY y DESC) AS tab;
]]></screen> ]]></screen>
But this approach is not guaranteed to work in all situations, and But this syntax is not allowed in the SQL standard, and is
it is not strictly SQL-conforming. A future version of PostgreSQL not portable to other database systems. A future version of
might provide an additional feature to control the order in a <productname>PostgreSQL</> might provide an additional feature to control
better-defined way (<literal>xmlagg(expr ORDER BY expr, expr, the order in a better-defined way (<literal>xmlagg(expr ORDER BY expr, expr,
...</literal>). ...)</literal>).
</para> </para>
<para> <para>