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Per-column collation support

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This adds collation support for columns and domains, a COLLATE clause
to override it per expression, and B-tree index support.

Peter Eisentraut
reviewed by Pavel Stehule, Itagaki Takahiro, Robert Haas, Noah Misch
This commit is contained in:
Peter Eisentraut
2011-02-08 23:04:18 +02:00
parent 1703f0e8da
commit 414c5a2ea6
156 changed files with 4519 additions and 582 deletions
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48
doc/src/sgml/syntax.sgml
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@@ -1899,6 +1899,54 @@ CAST ( <replaceable>expression</replaceable> AS <replaceable>type</replaceable>
</note>
</sect2>
<sect2 id="sql-syntax-collate-clause">
<title>COLLATE Clause</title>
<indexterm>
<primary>COLLATE</primary>
</indexterm>
<para>
The <literal>COLLATE</literal> clause overrides the collation of
an expression. It is appended to the expression it applies to:
<synopsis>
<replaceable>expr</replaceable> COLLATE <replaceable>collation</replaceable>
</synopsis>
where <replaceable>collation</replaceable> is a possibly
schema-qualified identifier. The <literal>COLLATE</literal>
clause binds tighter than operators; parentheses can be used when
necessary.
</para>
<para>
If no collation is explicitly specified, the database system
either derives a collation from the columns involved in the
expression, or it defaults to the default collation of the
database if no column is involved in the expression.
</para>
<para>
The two typical uses of the <literal>COLLATE</literal> clause are
overriding the sort order in an <literal>ORDER BY</> clause, for
example:
<programlisting>
SELECT a, b, c FROM tbl WHERE ... ORDER BY a COLLATE "C";
</programlisting>
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";
</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.
</para>
</sect2>
<sect2 id="sql-syntax-scalar-subqueries">
<title>Scalar Subqueries</title>