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<!-- $Header: /cvsroot/pgsql/doc/src/sgml/ref/create_conversion.sgml,v 1.4 2002/09/21 18:32:54 petere Exp $ -->
<refentry id="SQL-CREATECONVERSION">
<refmeta>
<refentrytitle id="SQL-CREATECONVERSION-TITLE">CREATE CONVERSION</refentrytitle>
<refmiscinfo>SQL - Language Statements</refmiscinfo>
</refmeta>
<refnamediv>
<refname>CREATE CONVERSION</refname>
<refpurpose>define a user-defined conversion</refpurpose>
</refnamediv>
<refsynopsisdiv>
<synopsis>
CREATE [DEFAULT] CONVERSION <replaceable>conversion_name</replaceable>
FOR <replaceable>source_encoding</replaceable>
TO <replaceable>dest_encoding</replaceable> FROM <replaceable>funcname</replaceable>
</synopsis>
</refsynopsisdiv>
<refsect1 id="sql-createconversion-description">
<title>Description</title>
<para>
<command>CREATE CONVERSION</command> defines a new encoding
conversion. There are two kinds of conversions. A default
conversion is used for an automatic encoding conversion between
frontend and backend. There should be only one default conversion
for source/destination encodings pair in a schema. None default
conversion never be used for the automatic conversion. Instead it
can be used for CONVERT() function.
</para>
<para>
To be able to create a conversion, you must have the execute right
on the function and the usage right on the schema the function
belongs to.
</para>
<variablelist>
<title>Parameters</title>
<varlistentry>
<term><literal>DEFAULT</literal></term>
<listitem>
<para>
The <literal>DEFAULT</> clause indicates that this conversion
is the default for this particular source to destination
encoding. There should be only one default encoding in a schema
for the encoding pair. A default encoding can be used for not
only CONVERT() function, but also for the automatic encoding
conversion between frontend and backend. For this purpose, two
conversions, from encoding A to B AND encoding B to A, must be
defined.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable>conversion_name</replaceable></term>
<listitem>
<para>
The name of the conversion. The conversion name may be
schema-qualified. If it is not, a conversion is defined in the
current schema. The conversion name must be unique with in a
schema.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable>source_encoding</replaceable></term>
<listitem>
<para>
The source encoding name.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable>source_encoding</replaceable></term>
<listitem>
<para>
The destination encoding name.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable>funcname</replaceable></term>
<listitem>
<para>
The function used to perform the conversion. The function name may
be schema-qualified. If it is not, the function will be looked
up in the path.
</para>
<para>
The function must have following signature:
<programlisting>
conv_proc(
INTEGER, -- source encoding id
INTEGER, -- destination encoding id
CSTRING, -- source string (null terminated C string)
CSTRING, -- destination string (null terminated C string)
INTEGER -- source string length
) returns VOID;
</programlisting>
</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1 id="sql-createconversion-notes">
<title>Notes</title>
<para>
Use <command>DROP CONVERSION</command> to remove user-defined conversions.
</para>
<para>
The privileges required to create a conversion may be changed in a future
release.
</para>
</refsect1>
<refsect1 id="sql-createconversion-examples">
<title>Examples</title>
<para>
To create a conversion from encoding UNICODE to LATIN1 using <function>myfunc</>:
<programlisting>
CREATE CONVERSION myconv FOR 'UNICODE' TO 'LATIN1' FROM myfunc;
</programlisting>
</para>
</refsect1>
<refsect1 id="sql-createconversion-compat">
<title>Compatibility</title>
<para>
<command>CREATE CONVERSION</command>
is a <productname>PostgreSQL</productname> extension.
There is no <command>CREATE CONVERSION</command>
statement in <acronym>SQL99</acronym>.
</para>
</refsect1>
<refsect1 id="sql-createconversion-seealso">
<title>See Also</title>
<para>
<xref linkend="sql-createfunction" endterm="sql-createfunction-title">,
<xref linkend="sql-dropconversion" endterm="sql-dropconversion-title">,
<citetitle>PostgreSQL Programmer's Guide</citetitle>
</para>
</refsect1>
</refentry>
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