SQLite 函数
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sqlite_create_function

SQLiteDatabase::createFunction

(PHP 5 < 5.4.0, sqlite >= 1.0.0)

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

说明

void sqlite_create_function ( resource $dbhandle , string $function_name , callable $callback [, int $num_args = -1 ] )

面向对象风格 (method):

public void SQLiteDatabase::createFunction ( string $function_name , callable $callback [, int $num_args = -1 ] )

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.

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

dbhandle

The SQLite Database resource; returned from sqlite_open() when used procedurally. This parameter is not required when using the object-oriented method.

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).

num_args

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

Note: 为兼容其他数据库扩展(比如 MySQL),支持两种可替代的语法。推荐第一种格式,函数的第一个参数是dbhandle

返回值

没有返回值。

范例

Example #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.

Example #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

Note:

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.

Tip

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.

Tip

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

参见


SQLite 函数
在线手册:中文  英文

用户评论:

Dodolidet (2011-07-19 22:44:39)

Although you can create an UDF named 'regexp()', I think it won't be registered as REGEXP operator..

<?php
//registering REGEXP
function my_sqlite_regexp($x,$y){
    return (int)
preg_match("`$y`i",$x);
}
echo 
$db->createFunction('regexp','my_sqlite_regexp',2);

//testing regexp as function, working
$res $db->query("SELECT * FROM x WHERE regexp(c,'h')"SQLITE_ASSOC $err) ;

//testing regexp as operator, not working, near "REGEXP": syntax error
$res $db->query("SELECT * FROM x WHERE c REGEXP 'h'"SQLITE_ASSOC $err); 
?>

I'd also swapped the function parameters $x and $y, but also not works..
-----
From SQLite documentation:
"The REGEXP operator is a special syntax for the regexp() user function. No regexp() user function is defined by default and so use of the REGEXP operator will normally result in an error message. If a application-defined SQL function named "regexp" is added at run-time, that function will be called in order to implement the REGEXP operator."

Brett (2005-05-20 10:27:55)

In my previous comment, there was an error in the code which was causing the issue.

Removing the surrounding quotes from from_unixtime()'s return value solved the issue, and so UDFs _do work_ from within DELETEs and INSERTs!  Yay!

<?php

// SQLite UDF
// Mimic MySQL FROM_UNIXTIME
function from_unixtime($unixtime)
{
    return 
date('Y-m-d H:i:s'$unixtime);  // no surrouding quotes
}

?>

Brett (2005-05-20 09:44:11)

It appears that UDFs created by sqlite_create_function() do not work properly within INSERT or DELETE statements.

A simplified INSERT example:

<?php

// SQLite UDF
// Mimic MySQL FROM_UNIXTIME function
function from_unixtime($unixtime)
{
    return 
"'".date('Y-m-d H:i:s'$unixtime)."'";
}

// -----------------------------------------------------------

// Open the database and create the UDF
$handle sqlite_open('db.sqlite'0666);
sqlite_create_function($handle'FROM_UNIXTIME''from_unixtime'1);

// Insert a row
$sql "
    INSERT INTO table (name, timestamp)
    VALUES ('Foo', FROM_UNIXTIME("
.time().");
    "
;

$result sqlite_exec($handle$sql);

// Retrieve the row
$sql     "SELECT * FROM table";
$result sqlite_unbuffered_query($handle$sql)
$row    sqlite_fetch_all($resultSQLITE_ASSOC);

// Dump
print_r($row);

?>

This will show:

Array
(
    [0] => Array
        (
            [name] => 'Foo'
            [timestamp] => -1
        )
)

The expected result for timestamp would be something like '2005-05-20 10:00:00'

info at myphp dot it (2004-12-28 13:52:34)

The function can be a method of a class:

<?php

class sqlite_function {

    function 
md5($value)
    {
        return 
md5($value);
    }

}

$dbhandle sqlite_open('SQLiteDB');

sqlite_create_function($dbhandle'md5', array('sqlite_function''md5'), 1);

// From now on, you can use md5 function inside your SQL statements

?>

It works fine :)

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