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Document sqlite specific functions for PDO.

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git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@195553 c90b9560-bf6c-de11-be94-00142212c4b1
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Wez Furlong 2005-09-09 03:25:37 +00:00
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commit 95f26c1563
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199
reference/pdo_sqlite/functions/PDO-sqliteCreateAggregate.xml Normal file
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<?xml version='1.0' encoding='iso-8859-1'?>
<!-- $Revision: 1.1 $ -->
<refentry id="function.PDO-sqliteCreateAggregate">
<refnamediv>
<refname>PDO::sqliteCreateAggregate</refname>
<refpurpose>
Registers an aggregating User Defined Function for use in SQL statements
</refpurpose>
</refnamediv>
<refsect1 role="description">
&reftitle.description;
<methodsynopsis>
<type>bool</type><methodname>PDO::sqliteCreateAggregate</methodname>
<methodparam><type>string</type><parameter>function_name</parameter></methodparam>
<methodparam><type>callback</type><parameter>step_func</parameter></methodparam>
<methodparam><type>callback</type><parameter>finalize_func</parameter></methodparam>
<methodparam choice="opt"><type>int</type><parameter>num_args</parameter></methodparam>
</methodsynopsis>
&warn.experimental.func;
<para>
<function>PDO::sqliteCreateAggregate</function> is similar to
<function>PDO::sqliteCreateFunction</function> except that it registers
functions that can be used to calculate a result aggregated across all the
rows of a query.
</para>
<para>
The key difference between this function and
<function>PDO::sqliteCreateFunction</function> is that two functions are
required to manage the aggregate; <parameter>step_func</parameter> is
called for each row of the result set. Your PHP function should
accumulate the result and store it into the aggregation context.
Once all the rows have been processed,
<parameter>finalize_func</parameter> will be called and it should then
take the data from the aggregation context and return the result.
Callback functions should return a type understood by SQLite (i.e.
<link linkend="language.types.intro">scalar type</link>).
</para>
</refsect1>
<refsect1 role="parameters">
&reftitle.parameters;
<para>
<variablelist>
<varlistentry>
<term><parameter>function_name</parameter></term>
<listitem>
<para>
The name of the function used in SQL statements.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>step_func</parameter></term>
<listitem>
<para>
Callback function called for each row of the result set.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>finalize_func</parameter></term>
<listitem>
<para>
Callback function to aggregate the "stepped" data from each row.
</para>
</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>
</refsect1>
<refsect1 role="examples">
&reftitle.examples;
<para>
<example>
<title>max_length aggregation function example</title>
<programlisting role="php">
<![CDATA[
<?php
$data = array(
'one',
'two',
'three',
'four',
'five',
'six',
'seven',
'eight',
'nine',
'ten',
);
$db = new PDO('sqlite::memory:');
$db->exec("CREATE TABLE strings(a)");
$insert = $db->prepare('INSERT INTO strings VALUES (?)');
foreach ($data as $str) {
$insert->execute(array($str));
}
$insert = null;
function max_len_step(&$context, $string)
{
if (strlen($string) > $context) {
$context = strlen($string);
}
}
function max_len_finalize(&$context)
{
return $context;
}
$db->sqliteCreateAggregate('max_len', 'max_len_step', 'max_len_finalize');
var_dump($db->query('SELECT max_len(a) from strings')->fetchAll());
?>
]]>
</programlisting>
</example>
</para>
<para>
In this example, we are creating an aggregating function that will
calculate the length of the longest string in one of the columns of the
table. For each row, the <literal>max_len_step</literal> function is
called and passed a <parameter>context</parameter> parameter. The context
parameter is just like any other PHP variable and be set to hold an array
or even an object value. In this example, we are simply using it to hold
the maximum length we have seen so far; if the
<parameter>string</parameter> has a length longer than the current
maximum, we update the context to hold this new maximum length.
</para>
<para>
After all of the rows have been processed, SQLite calls the
<literal>max_len_finalize</literal> function to determine the aggregate
result. Here, we could perform some kind of calculation based on the
data found in the <parameter>context</parameter>. In our simple example
though, we have been calculating the result as the query progressed, so we
simply need to return the context value.
</para>
<tip>
<para>
It is NOT recommended for you to store a copy of the values in the context
and then process them at the end, as you would cause SQLite to use a lot of
memory to process the query - just think of how much memory you would need
if a million rows were stored in memory, each containing a string 32 bytes
in length.
</para>
</tip>
<tip>
<para>
You can use <function>PDO::sqliteCreateFunction</function> and
<function>PDO::sqliteCreateAggregate</function> to override SQLite native
SQL functions.
</para>
</tip>
</refsect1>
<refsect1 role="seealso">
&reftitle.seealso;
<para>
<simplelist>
<member><function>PDO::sqliteCreateFunction</function></member>
</simplelist>
</para>
</refentry>
<!-- Keep this comment at the end of the file
Local variables:
mode: sgml
sgml-omittag:t
sgml-shorttag:t
sgml-minimize-attributes:nil
sgml-always-quote-attributes:t
sgml-indent-step:1
sgml-indent-data:t
indent-tabs-mode:nil
sgml-parent-document:nil
sgml-default-dtd-file:"../../../../manual.ced"
sgml-exposed-tags:nil
sgml-local-catalogs:nil
sgml-local-ecat-files:nil
End:
vim600: syn=xml fen fdm=syntax fdl=2 si
vim: et tw=78 syn=sgml
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-->

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reference/pdo_sqlite/functions/PDO-sqliteCreateFunction.xml Normal file
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<?xml version='1.0' encoding='iso-8859-1'?>
<!-- $Revision: 1.1 $ -->
<refentry id="function.PDO-sqliteCreateFunction">
<refnamediv>
<refname>PDO::sqliteCreateFunction</refname>
<refpurpose>
Registers a User Defined Function for use in SQL statements
</refpurpose>
</refnamediv>
<refsect1 role="description">
&reftitle.description;
<methodsynopsis>
<type>bool</type><methodname>PDO::sqliteCreateFunction</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>
&warn.experimental.func;
<para>
<function>PDO::sqliteCreateFunction</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>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>PDO::sqliteCreateFunction</function> example</title>
<programlisting role="php">
<![CDATA[
<?php
function md5_and_reverse($string)
{
return strrev(md5($string));
}
$db = new PDO('sqlite:sqlitedb');
$db->sqliteCreateFunction('md5rev', 'md5_and_reverse', 1);
$rows = $db->query('SELECT md5rev(filename) FROM files')->fetchAll();
?>
]]>
</programlisting>
</example>
</para>
<para>
In this example, we have a function that calculates the md5 sum of a
string, and then reverses it. When the SQL statement executes, it
returns the value of the filename transformed by our function. The data
returned in <parameter>$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>
<!-- not for PDO it doesn't, at least not yet
<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 = $db->query("SELECT php('md5', filename) from files")->fetchAll();
?>
]]>
</programlisting>
<para>
This example will call the <function>md5</function> on each
<literal>filename</literal> column in the database and return the result
into <parameter>$rows</parameter>
</para>
</example>
</para>
-->
<tip>
<para>
You can use <function>PDO::sqliteCreateFunction</function> and
<function>PDO::sqliteCreateAggregate</function> to override SQLite native
SQL functions.
</para>
</tip>
</refsect1>
<refsect1 role="seealso">
&reftitle.seealso;
<para>
<simplelist>
<member><function>PDO::sqliteCreateAggregate</function></member>
</simplelist>
</para>
</refentry>
<!-- Keep this comment at the end of the file
Local variables:
mode: sgml
sgml-omittag:t
sgml-shorttag:t
sgml-minimize-attributes:nil
sgml-always-quote-attributes:t
sgml-indent-step:1
sgml-indent-data:t
indent-tabs-mode:nil
sgml-parent-document:nil
sgml-default-dtd-file:"../../../../manual.ced"
sgml-exposed-tags:nil
sgml-local-catalogs:nil
sgml-local-ecat-files:nil
End:
vim600: syn=xml fen fdm=syntax fdl=2 si
vim: et tw=78 syn=sgml
vi: ts=1 sw=1
-->