190 lines
5.2 KiB
Plaintext
190 lines
5.2 KiB
Plaintext
<!--
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doc/src/sgml/ref/create_conversion.sgml
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PostgreSQL documentation
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-->
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<refentry id="sql-createconversion">
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<indexterm zone="sql-createconversion">
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<primary>CREATE CONVERSION</primary>
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</indexterm>
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<refmeta>
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<refentrytitle>CREATE CONVERSION</refentrytitle>
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<manvolnum>7</manvolnum>
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<refmiscinfo>SQL - Language Statements</refmiscinfo>
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</refmeta>
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<refnamediv>
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<refname>CREATE CONVERSION</refname>
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<refpurpose>define a new encoding conversion</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<synopsis>
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CREATE [ DEFAULT ] CONVERSION <replaceable>name</replaceable>
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FOR <replaceable>source_encoding</replaceable> TO <replaceable>dest_encoding</replaceable> FROM <replaceable>function_name</replaceable>
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</synopsis>
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</refsynopsisdiv>
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<refsect1 id="sql-createconversion-description">
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<title>Description</title>
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<para>
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<command>CREATE CONVERSION</command> defines a new conversion between
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two character set encodings.
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</para>
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<para>
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Conversions that are marked <literal>DEFAULT</literal> can be used for
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automatic encoding conversion between client and server. To support that
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usage, two conversions, from encoding A to B <emphasis>and</emphasis>
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from encoding B to A, must be defined.
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</para>
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<para>
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To be able to create a conversion, you must have <literal>EXECUTE</literal> privilege
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on the function and <literal>CREATE</literal> privilege on the destination schema.
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</para>
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</refsect1>
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<refsect1>
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<title>Parameters</title>
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<variablelist>
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<varlistentry>
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<term><literal>DEFAULT</literal></term>
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<listitem>
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<para>
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The <literal>DEFAULT</literal> clause indicates that this conversion
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is the default for this particular source to destination
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encoding. There should be only one default encoding in a schema
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for the encoding pair.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable>name</replaceable></term>
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<listitem>
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<para>
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The name of the conversion. The conversion name can be
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schema-qualified. If it is not, the conversion is defined in the
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current schema. The conversion name must be unique within a
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schema.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable>source_encoding</replaceable></term>
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<listitem>
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<para>
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The source encoding name.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable>dest_encoding</replaceable></term>
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<listitem>
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<para>
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The destination encoding name.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable>function_name</replaceable></term>
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<listitem>
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<para>
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The function used to perform the conversion. The function name can
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be schema-qualified. If it is not, the function will be looked
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up in the path.
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</para>
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<para>
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The function must have the following signature:
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<programlisting>
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conv_proc(
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integer, -- source encoding ID
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integer, -- destination encoding ID
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cstring, -- source string (null terminated C string)
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internal, -- destination (fill with a null terminated C string)
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integer, -- source string length
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boolean -- if true, don't throw an error if conversion fails
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) RETURNS integer;
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</programlisting>
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The return value is the number of source bytes that were successfully
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converted. If the last argument is false, the function must throw an
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error on invalid input, and the return value is always equal to the
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source string length.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1 id="sql-createconversion-notes">
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<title>Notes</title>
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<para>
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Neither the source nor the destination encoding can
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be <literal>SQL_ASCII</literal>, as the server's behavior for cases
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involving the <literal>SQL_ASCII</literal> <quote>encoding</quote> is
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hard-wired.
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</para>
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<para>
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Use <command>DROP CONVERSION</command> to remove user-defined conversions.
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</para>
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<para>
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The privileges required to create a conversion might be changed in a future
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release.
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</para>
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</refsect1>
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<refsect1 id="sql-createconversion-examples">
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<title>Examples</title>
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<para>
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To create a conversion from encoding <literal>UTF8</literal> to
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<literal>LATIN1</literal> using <function>myfunc</function>:
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<programlisting>
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CREATE CONVERSION myconv FOR 'UTF8' TO 'LATIN1' FROM myfunc;
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</programlisting></para>
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</refsect1>
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<refsect1 id="sql-createconversion-compat">
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<title>Compatibility</title>
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<para>
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<command>CREATE CONVERSION</command>
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is a <productname>PostgreSQL</productname> extension.
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There is no <command>CREATE CONVERSION</command>
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statement in the SQL standard, but a <command>CREATE TRANSLATION</command>
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statement that is very similar in purpose and syntax.
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</para>
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</refsect1>
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<refsect1 id="sql-createconversion-seealso">
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<title>See Also</title>
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<simplelist type="inline">
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<member><xref linkend="sql-alterconversion"/></member>
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<member><xref linkend="sql-createfunction"/></member>
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<member><xref linkend="sql-dropconversion"/></member>
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</simplelist>
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</refsect1>
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</refentry>
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