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A bit more editing for collation documentation.

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This commit is contained in:
Tom Lane 2011-03-08 22:50:15 -05:00
parent d367d41d66
commit c0dc44ebba
1 changed files with 30 additions and 11 deletions
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doc/src/sgml/syntax.sgml
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@ -1257,6 +1257,12 @@ SELECT 3 OPERATOR(pg_catalog.+) 4;
</para> </para>
</listitem> </listitem>
<listitem>
<para>
A collation expression
</para>
</listitem>
<listitem> <listitem>
<para> <para>
A scalar subquery A scalar subquery
@ -1898,8 +1904,8 @@ CAST ( <replaceable>expression</replaceable> AS <replaceable>type</replaceable>
</note> </note>
</sect2> </sect2>
<sect2 id="sql-syntax-collate-clause"> <sect2 id="sql-syntax-collate-exprs">
<title>COLLATE Clause</title> <title>Collation Expressions</title>
<indexterm> <indexterm>
<primary>COLLATE</primary> <primary>COLLATE</primary>
@ -1925,7 +1931,7 @@ CAST ( <replaceable>expression</replaceable> AS <replaceable>type</replaceable>
</para> </para>
<para> <para>
The two typical uses of the <literal>COLLATE</literal> clause are The two common uses of the <literal>COLLATE</literal> clause are
overriding the sort order in an <literal>ORDER BY</> clause, for overriding the sort order in an <literal>ORDER BY</> clause, for
example: example:
<programlisting> <programlisting>
@ -1934,15 +1940,28 @@ SELECT a, b, c FROM tbl WHERE ... ORDER BY a COLLATE "C";
and overriding the collation of a function or operator call that and overriding the collation of a function or operator call that
has locale-sensitive results, for example: has locale-sensitive results, for example:
<programlisting> <programlisting>
SELECT * FROM tbl WHERE a > 'foo' COLLATE "C"; SELECT * FROM tbl WHERE a &gt; 'foo' COLLATE "C";
</programlisting> </programlisting>
In the latter case it doesn't matter which argument of the Note that in the latter case the <literal>COLLATE</> clause is
operator of function call the <literal>COLLATE</> clause is attached to an input argument of the operator we wish to affect.
attached to, because the collation that is applied by the operator It doesn't matter which argument of the operator or function call the
or function is derived from all arguments, and <literal>COLLATE</> clause is attached to, because the collation that is
the <literal>COLLATE</> clause will override the collations of all applied by the operator or function is derived by considering all
other arguments. Attaching nonmatching <literal>COLLATE</> arguments, and an explicit <literal>COLLATE</> clause will override the
clauses to more than one argument, however, is an error. collations of all other arguments. (Attaching non-matching
<literal>COLLATE</> clauses to more than one argument, however, is an
error. For more details see <xref linkend="collation">.)
Thus, this gives the same result as the previous example:
<programlisting>
SELECT * FROM tbl WHERE a COLLATE "C" &gt; 'foo';
</programlisting>
But this is an error:
<programlisting>
SELECT * FROM tbl WHERE (a &gt; 'foo') COLLATE "C";
</programlisting>
because it attempts to apply a collation to the result of the
<literal>&gt;</> operator, which is of the non-collatable data type
<type>boolean</>.
</para> </para>
</sect2> </sect2>