postgresql/doc/src/sgml/ref/create_conversion.sgml

<!-- $PostgreSQL: pgsql/doc/src/sgml/ref/create_conversion.sgml,v 1.23 2010/04/03 07:22:58 petere Exp $ -->

<refentry id="SQL-CREATECONVERSION">
 <refmeta>
  <refentrytitle>CREATE CONVERSION</refentrytitle>
  <manvolnum>7</manvolnum>
  <refmiscinfo>SQL - Language Statements</refmiscinfo>
 </refmeta>

 <refnamediv>
  <refname>CREATE CONVERSION</refname>
  <refpurpose>define a new encoding conversion</refpurpose>
 </refnamediv>

 <indexterm zone="sql-createconversion">
  <primary>CREATE CONVERSION</primary>
 </indexterm>

 <refsynopsisdiv>
<synopsis>
CREATE [ DEFAULT ] CONVERSION <replaceable>name</replaceable>
    FOR <replaceable>source_encoding</replaceable> TO <replaceable>dest_encoding</replaceable> FROM <replaceable>function_name</replaceable>
</synopsis>
 </refsynopsisdiv>
  
 <refsect1 id="sql-createconversion-description">
  <title>Description</title>

  <para>
   <command>CREATE CONVERSION</command> defines a new conversion between
   character set encodings.  Also, conversions that
   are marked <literal>DEFAULT</> can be used for automatic encoding
   conversion between
   client and server. For this purpose, two conversions, from encoding A to
   B <emphasis>and</emphasis> from encoding B to A, must be defined.
 </para>

  <para>
   To be able to create a conversion, you must have <literal>EXECUTE</literal> privilege
   on the function and <literal>CREATE</literal> privilege on the destination schema.
  </para>
 </refsect1>


 <refsect1>
  <title>Parameters</title>

   <variablelist>
    <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.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><replaceable>name</replaceable></term>

     <listitem>
      <para>
       The name of the conversion. The conversion name can be
       schema-qualified. If it is not, the conversion is defined in the
       current schema. The conversion name must be unique within a
       schema.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><replaceable>source_encoding</replaceable></term>

     <listitem>
      <para>
       The source encoding name.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><replaceable>dest_encoding</replaceable></term>

     <listitem>
      <para>
       The destination encoding name.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><replaceable>function_name</replaceable></term>

     <listitem>
      <para>
       The function used to perform the conversion.  The function name can
       be schema-qualified.  If it is not, the function will be looked
       up in the path.
      </para>

      <para>
       The function must have the following signature:

<programlisting>
conv_proc(
    integer,  -- source encoding ID
    integer,  -- destination encoding ID
    cstring,  -- source string (null terminated C string)
    internal, -- destination (fill with a 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 might be changed in a future
   release.
  </para>
 </refsect1>

 <refsect1 id="sql-createconversion-examples">
  <title>Examples</title>

  <para>
   To create a conversion from encoding <literal>UTF8</literal> to
   <literal>LATIN1</literal> using <function>myfunc</>:
<programlisting>
CREATE CONVERSION myconv FOR 'UTF8' 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 the SQL standard.
  </para>
 </refsect1>


 <refsect1 id="sql-createconversion-seealso">
  <title>See Also</title>

  <simplelist type="inline">
   <member><xref linkend="sql-alterconversion"></member>
   <member><xref linkend="sql-createfunction"></member>
   <member><xref linkend="sql-dropconversion"></member>
  </simplelist>
 </refsect1>

</refentry>