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# sqlite_create_function

(PHP 5)

sqlite_create_function -- Registers a "regular" User Defined Function for use in SQL statements

## Description

bool sqlite_create_function ( resource dbhandle, string function_name, mixed callback [, int num_args])

sqlite_create_function() 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.

dbhandle specifies the database handle that you wish to extend, function_name specifies the name of the function that you will use in your SQL statements, callback is any valid PHP callback to specify a PHP function that should be called to handle the SQL function. The optional parameter num_args is used as a hint by the SQLite expression parser/evaluator. It is recommended that you specify a value if your function will only ever accept a fixed number of parameters.

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

示範 1.sqlite_create_function() example
`<?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; } ?>`

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.

PHP registers a special function named php when the database is first opened. The php function can be used to call any PHP function without having to register it first.

示範 2.Example of using the PHP function
`<?php $rows = sqlite_array_query($dbhandle, "SELECT php('md5', filename) from files"); ?>`
This example will call the md5() on each filename column in the database and return the result into $rows

> 備注: 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 sqlite_udf_encode_binary() and sqlite_udf_decode_binary() for more details.

> 心得: 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.

> 心得: You can use sqlite_create_function() and sqlite_create_aggregate() to override SQLite native SQL functions.

See also sqlite_create_aggregate().

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