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<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision: 297028 $ -->
<refentry xml:id="function.sqlite-create-function" xmlns="http://docbook.org/ns/docbook">
<refnamediv>
<refname>sqlite_create_function</refname>
<refname>SQLiteDatabase->createFunction</refname>
<refpurpose>
Registers a "regular" User Defined Function for use in SQL statements
</refpurpose>
</refnamediv>
<refsect1 role="description">
&reftitle.description;
<methodsynopsis>
<type>void</type><methodname>sqlite_create_function</methodname>
<methodparam><type>resource</type><parameter>dbhandle</parameter></methodparam>
<methodparam><type>string</type><parameter>function_name</parameter></methodparam>
<methodparam><type>callback</type><parameter>callback</parameter></methodparam>
<methodparam choice="opt"><type>int</type><parameter>num_args</parameter><initializer>-1</initializer></methodparam>
</methodsynopsis>
<para>Object oriented style (method):</para>
<classsynopsis>
<ooclass><classname>SQLiteDatabase</classname></ooclass>
<methodsynopsis>
<type>void</type><methodname>createFunction</methodname>
<methodparam><type>string</type><parameter>function_name</parameter></methodparam>
<methodparam><type>callback</type><parameter>callback</parameter></methodparam>
<methodparam choice="opt"><type>int</type><parameter>num_args</parameter><initializer>-1</initializer></methodparam>
</methodsynopsis>
</classsynopsis>
<para>
<function>sqlite_create_function</function> allows you to register a PHP
function with SQLite as an <acronym>UDF</acronym> (User Defined
Function), so that it can be called from within your SQL statements.
</para>
<para>
The UDF can be used in any SQL statement that can call functions, such as
SELECT and UPDATE statements and also in triggers.
</para>
</refsect1>
<refsect1 role="parameters">
&reftitle.parameters;
<para>
<variablelist>
<varlistentry>
<term><parameter>dbhandle</parameter></term>
<listitem>
<para>
The SQLite Database resource; returned from <function>sqlite_open</function>
when used procedurally. This parameter is not required
when using the object-oriented method.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>function_name</parameter></term>
<listitem>
<para>
The name of the function used in SQL statements.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>callback</parameter></term>
<listitem>
<para>
Callback function to handle the defined SQL function.
</para>
<note>
<simpara>
Callback functions should return a type understood by SQLite (i.e.
<link linkend="language.types.intro">scalar type</link>).
</simpara>
</note>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>num_args</parameter></term>
<listitem>
<para>
Hint to the SQLite parser if the callback function accepts a
predetermined number of arguments.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
&sqlite.param-compat;
</refsect1>
<refsect1 role="returnvalues">
&reftitle.returnvalues;
<para>
&return.void;
</para>
</refsect1>
<refsect1 role="examples">
&reftitle.examples;
<para>
<example>
<title><function>sqlite_create_function</function> example</title>
<programlisting role="php">
<![CDATA[
<?php
function md5_and_reverse($string)
{
return strrev(md5($string));
}
if ($dbhandle = sqlite_open('mysqlitedb', 0666, $sqliteerror)) {
sqlite_create_function($dbhandle, 'md5rev', 'md5_and_reverse', 1);
$sql = 'SELECT md5rev(filename) FROM files';
$rows = sqlite_array_query($dbhandle, $sql);
} else {
echo 'Error opening sqlite db: ' . $sqliteerror;
exit;
}
?>
]]>
</programlisting>
</example>
</para>
<para>
In this example, we have a function that calculates the md5 sum of a
string, and then reverses it. When the SQL statement executes, it
returns the value of the filename transformed by our function. The data
returned in <parameter>$rows</parameter> contains the processed result.
</para>
<para>
The beauty of this technique is that you do not need to process the
result using a &foreach; loop after you have queried for the data.
</para>
<para>
PHP registers a special function named <literal>php</literal> when the
database is first opened. The php function can be used to call any PHP
function without having to register it first.
</para>
<para>
<example>
<title>Example of using the PHP function</title>
<programlisting role="php">
<![CDATA[
<?php
$rows = sqlite_array_query($dbhandle, "SELECT php('md5', filename) from files");
?>
]]>
</programlisting>
<para>
This example will call the <function>md5</function> on each
<literal>filename</literal> column in the database and return the result
into <parameter>$rows</parameter>
</para>
</example>
</para>
<note>
<para>
For performance reasons, PHP will not automatically encode/decode binary
data passed to and from your UDF's. You need to manually encode/decode
the parameters and return values if you need to process binary data in
this way. Take a look at <function>sqlite_udf_encode_binary</function>
and <function>sqlite_udf_decode_binary</function> for more details.
</para>
</note>
<tip>
<para>
It is not recommended to use UDF's to handle processing of
binary data, unless high performance is not a key requirement of your
application.
</para>
</tip>
<tip>
<para>
You can use <function>sqlite_create_function</function> and
<function>sqlite_create_aggregate</function> to override SQLite native
SQL functions.
</para>
</tip>
</refsect1>
<refsect1 role="seealso">
&reftitle.seealso;
<para>
<simplelist>
<member><function>sqlite_create_aggregate</function></member>
</simplelist>
</para>
</refsect1>
</refentry>
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