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<refentry id="function.sqlite-create-function">
 <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></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></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="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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