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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>
</listitem>
<listitem>
<para>
A collation expression
</para>
</listitem>
<listitem>
<para>
A scalar subquery
@ -1898,8 +1904,8 @@ CAST ( <replaceable>expression</replaceable> AS <replaceable>type</replaceable>
</note>
</sect2>
<sect2 id="sql-syntax-collate-clause">
<title>COLLATE Clause</title>
<sect2 id="sql-syntax-collate-exprs">
<title>Collation Expressions</title>
<indexterm>
<primary>COLLATE</primary>
@ -1925,7 +1931,7 @@ CAST ( <replaceable>expression</replaceable> AS <replaceable>type</replaceable>
</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
example:
<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
has locale-sensitive results, for example:
<programlisting>
SELECT * FROM tbl WHERE a > 'foo' COLLATE "C";
SELECT * FROM tbl WHERE a &gt; 'foo' COLLATE "C";
</programlisting>
In the latter case it doesn't matter which argument of the
operator of function call the <literal>COLLATE</> clause is
attached to, because the collation that is applied by the operator
or function is derived from all arguments, and
the <literal>COLLATE</> clause will override the collations of all
other arguments. Attaching nonmatching <literal>COLLATE</>
clauses to more than one argument, however, is an error.
Note that in the latter case the <literal>COLLATE</> clause is
attached to an input argument of the operator we wish to affect.
It doesn't matter which argument of the operator or function call the
<literal>COLLATE</> clause is attached to, because the collation that is
applied by the operator or function is derived by considering all
arguments, and an explicit <literal>COLLATE</> clause will override the
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>
</sect2>