postgres/doc/src/sgml/ref/create_conversion.sgml

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<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.  Conversion names may be used in the CONVERT() function
   to specify a particular encoding conversion.  Also, conversions that
   are marked DEFAULT can be used for automatic encoding conversion between
   frontend and backend. For this purpose, two conversions, from encoding A to
   B AND from encoding B to A, must be defined.
 </para>

  <para>
   To be able to create a conversion, you must have the execute right
   on the function and the create right on the destination schema.
  </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.
      </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, 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>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 the 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">,
   &cite-programmer;
  </para>
 </refsect1>

</refentry>

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