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Marginal tweaks in the documentation for ORDER BY; in particular point

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out the common error that ORDER BY x, y DESC does not mean the same as
ORDER BY x DESC, y DESC.
This commit is contained in:
Tom Lane 2007-01-09 16:59:20 +00:00
parent 69db009163
commit 1e0bf9041e
2 changed files with 22 additions and 9 deletions
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9
doc/src/sgml/queries.sgml
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@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/queries.sgml,v 1.40 2007/01/09 02:14:10 tgl Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/queries.sgml,v 1.41 2007/01/09 16:59:20 tgl Exp $ -->
<chapter id="queries">
<title>Queries</title>
@ -1262,6 +1262,13 @@ SELECT a, b FROM table1 ORDER BY a + b, c;
<literal>DESC</> order, and <literal>NULLS LAST</> otherwise.
</para>
<para>
Note that the ordering options are considered independently for each
sort column. For example <literal>ORDER BY x, y DESC</> means
<literal>ORDER BY x ASC, y DESC</>, which is not the same as
<literal>ORDER BY x DESC, y DESC</>.
</para>
<para>
For backwards compatibility with the SQL92 version of the standard,
a <replaceable>sort_expression</> can instead be the name or number

22
doc/src/sgml/ref/select.sgml
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@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/ref/select.sgml,v 1.95 2007/01/09 02:14:10 tgl Exp $
$PostgreSQL: pgsql/doc/src/sgml/ref/select.sgml,v 1.96 2007/01/09 16:59:20 tgl Exp $
PostgreSQL documentation
-->
@ -644,13 +644,6 @@ HAVING <replaceable class="parameter">condition</replaceable>
<synopsis>
ORDER BY <replaceable class="parameter">expression</replaceable> [ ASC | DESC | USING <replaceable class="parameter">operator</replaceable> ] [ NULLS { FIRST | LAST } ] [, ...]
</synopsis>
<replaceable class="parameter">expression</replaceable> can be the
name or ordinal number of an output column
(<command>SELECT</command> list item), or it can be an arbitrary
expression formed from input-column values.
</para>
<para>
The <literal>ORDER BY</literal> clause causes the result rows to
be sorted according to the specified expression(s). If two rows are
equal according to the leftmost expression, they are compared
@ -659,6 +652,13 @@ ORDER BY <replaceable class="parameter">expression</replaceable> [ ASC | DESC |
an implementation-dependent order.
</para>
<para>
Each <replaceable class="parameter">expression</replaceable> can be the
name or ordinal number of an output column
(<command>SELECT</command> list item), or it can be an arbitrary
expression formed from input-column values.
</para>
<para>
The ordinal number refers to the ordinal (left-to-right) position
of the result column. This feature makes it possible to define an
@ -717,6 +717,12 @@ SELECT name FROM distributors ORDER BY code;
on whether the operator is a less-than or greater-than operator.
</para>
<para>
Note that ordering options apply only to the expression they follow;
for example <literal>ORDER BY x, y DESC</> does not mean
the same thing as <literal>ORDER BY x DESC, y DESC</>.
</para>
<para>
Character-string data is sorted according to the locale-specific
collation order that was established when the database cluster