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# PDO::sqliteCreateFunction

(no version information, might be only in CVS)

PDO::sqliteCreateFunction -- Registers a User Defined Function for use in SQL statements

## 说明

bool PDO::sqliteCreateFunction ( string function_name, callback callback [, int num_args] )

警告
本函数是实验性的。本函数的行为，包括函数名称以及其它任何关于本函数的文档可能会在没有通知的情况下随 PHP 以后的发布而改变。使用本函数风险自担。

PDO::sqliteCreateFunction() 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.

## 参数

function_name

  The name of the function used in SQL statements.

callback

  Callback function to handle the defined SQL function.

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

num_args

  Hint to the SQLite parser if the callback function accepts a predetermined number of arguments.

> 注: 为兼容其它数据库（例如 MySQL），支持另两种替代的语法。推荐用第一种，dbhandle 参数作为函数的第一个参数。

## 范例

例子 1. PDO::sqliteCreateFunction() example

`<?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(); ?>`

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.

> 提示: You can use PDO::sqliteCreateFunction() and PDO::sqliteCreateAggregate() to override SQLite native SQL functions.

> 注: This method is not available with the SQLite2 driver. Use the old style sqlite API for that instead.

## 参见

PDO::sqliteCreateAggregate()
sqlite_create_function()
sqlite_create_aggregate()

后退 | 起点 | 前进
PDO::sqliteCreateAggregate | 上一级 | Standard PHP Library (SPL) Functions