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Many thanks to Johann :) git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@132642 c90b9560-bf6c-de11-be94-00142212c4b1
126 lines
4.4 KiB
XML
126 lines
4.4 KiB
XML
<?xml version="1.0" encoding="iso-8859-1"?>
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<!-- $Revision: 1.1 $ -->
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<refentry id="function.sqlite-create-function">
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<refnamediv>
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<refname>sqlite_create_function</refname>
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<refpurpose>Registers a "regular" User Defined Function for use in SQL statements</refpurpose>
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</refnamediv>
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<refsect1>
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<title>Description</title>
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<methodsynopsis>
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<type>bool</type><function>sqlite_create_function</function>
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<methodparam><type>resource</type><parameter>db</parameter></methodparam>
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<methodparam><type>string</type><parameter>function_name</parameter></methodparam>
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<methodparam><type>mixed</type><parameter>callback</parameter></methodparam>
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<methodparam choice="opt"><type>int</type><parameter>num_args</parameter></methodparam>
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</methodsynopsis>
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<para>
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<function>sqlite_create_function</function> allows you to register a PHP
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function with SQLite as an <acronym>UDF</acronym> (User Defined
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Function), so that it can be called from within your SQL
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statements.
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</para>
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<para>
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<parameter>db</parameter> specifies the database handle that you wish to
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extend, <parameter>function_name</parameter> specifies the name of the
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function that you will use in your SQL statements,
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<parameter>callback</parameter> is any valid PHP callback to specify a
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PHP function that should be called to handle the SQL function.
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The optional parameter <parameter>num_args</parameter> is used as a hint
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by the SQLite expression parser/evaluator. It is recommended that you
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specifiy a value if your function will only ever accept a fixed number of
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parameters.
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</para>
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<para>
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The UDF can be used in any SQL statement that can call functions, such as
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SELECT and UPDATE statements and also in triggers.
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</para>
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<example>
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<title><function>sqlite_create_function</function> example</title>
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<programlisting role="php">
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<![CDATA[
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<?php
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function md5_and_reverse($string)
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{
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return strrev(md5($string));
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}
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sqlite_create_function($db, 'md5rev', 'md5_and_reverse', 1);
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$rows = sqlite_array_query($db, 'SELECT md5rev(filename) from files');
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?>]]>
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</programlisting>
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<para>
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In this example, we have a function that calculates the md5 sum of a
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string, and then reverses it. When the SQL statement executes, it
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returns the value of the filename transformed by our function. The data
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returned in <parameter>$rows</parameter> contains the processed result.
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</para>
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<para>
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The beauty of this technique is that you do not need to process the
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result using a foreach() loop after you have queried for the data.
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</para>
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</example>
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<note>
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<para>
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PHP registers a special function named <literal>php</literal> when the
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database is first opened. The php function can be used to call any PHP
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function without having to register it first.
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</para>
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</note>
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<example>
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<title>Example of using the PHP function</title>
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<programlisting role="php">
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<![CDATA[
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<?php
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$rows = sqlite_array_query($db, "SELECT php('md5', filename) from files");
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?>]]>
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</programlisting>
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<para>
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This example will call the <function>md5</function> on each
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<literal>filename</literal> column in the database and return the result
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into <parameter>$rows</parameter>
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</para>
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</example>
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<note>
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<para>
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For performance reasons, PHP will not automatically encode/decode binary
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data passed to and from your UDF's. You need to manually encode/decode
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the parameters and return values if you need to process binary data in
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this way.
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</para>
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<para>
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<emphasis>It is not recommended to use UDF's to handle processesing of
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binary data, unless high performance is not a key requirement of your
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application.
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</emphasis>
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</para>
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</note>
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<para>
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See also <function>sqlite_register_aggregate</function>.
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</para>
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</refsect1>
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</refentry>
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<!-- Keep this comment at the end of the file
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Local variables:
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mode: sgml
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sgml-omittag:t
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sgml-shorttag:t
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sgml-minimize-attributes:nil
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sgml-always-quote-attributes:t
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sgml-indent-step:1
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sgml-indent-data:t
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sgml-parent-document:nil
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sgml-default-dtd-file:"../../manual.ced"
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sgml-exposed-tags:nil
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sgml-local-catalogs:nil
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sgml-local-ecat-files:nil
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End:
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vim600: syn=xml fen fdm=syntax fdl=2 si
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vim: et tw=78 syn=sgml
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vi: ts=1 sw=1
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-->
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