PHP Manual: Registers a User Defined Function for use in SQL statements

Description

public bool PDO::sqliteCreateFunction(
    string $function_name,
    callable $callback,
    int $num_args = -1,
    int $flags = 0
)

Warning

This function is EXPERIMENTAL. The behaviour of this function, its name, and surrounding documentation may change without notice in a future release of PHP. This function should be used at your own risk.

This method allows you to register a PHP function with SQLite as an UDF (User Defined Function), so that it can be called from within your SQL statements.

The UDF can be used in any SQL statement that can call functions, such as SELECT and UPDATE statements and also in triggers.

Parameters

function_name

The name of the function used in SQL statements.

callback

Callback function to handle the defined SQL function.

Note: Callback functions should return a type understood by SQLite (i.e. scalar type).

This function need to be defined as:

mixed callback(mixed $value, mixed ...$values)

value: The first argument passed to the SQL function.
values: Further arguments passed to the SQL function.

num_args

The number of arguments that the SQL function takes. If this parameter is -1, then the SQL function may take any number of arguments.

flags

A bitwise conjunction of flags. Currently, only PDO::SQLITE_DETERMINISTIC is supported, which specifies that the function always returns the same result given the same inputs within a single SQL statement.

Return Values

Returns true on success or false on failure.

Changelog

Version	Description
7.1.4	The `flags` parameter has been added.

Examples

Example #1 PDO::sqliteCreateFunction example

<?php
function md5_and_reverse($string) 
{
    return strrev(hash('md5', $string));
}

$db = new PDO('sqlite:sqlitedb');
$db->sqliteCreateFunction('md5rev', 'md5_and_reverse', 1);
$rows = $db->query('SELECT md5rev(filename) FROM files')->fetchAll();
?>

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 $rows contains the processed result.

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.

Tip

You can use PDO::sqliteCreateFunction and PDO::sqliteCreateAggregate to override SQLite native SQL functions.