PHP - Manual: PDO::sqliteCreateAggregate

2024-11-14

PDO::sqliteCreateAggregate

(PHP 5 >= 5.1.0, PHP 7, PHP 8, PECL pdo_sqlite >= 1.0.0)

PDO::sqliteCreateAggregate — Registers an aggregating User Defined Function for use in SQL statements

说明

public PDO::sqliteCreateAggregate(
    string $function_name,
    callable $step_func,
    callable $finalize_func,
    int $num_args = ?
): bool

警告

此函数是实验性的。此函数的表象，包括名称及其相关文档都可能在未来的 PHP 发布版本中未通知就被修改。使用本函数风险自担。

This method is similar to PDO::sqliteCreateFunction except that it registers functions that can be used to calculate a result aggregated across all the rows of a query.

The key difference between this method and PDO::sqliteCreateFunction is that two functions are required to manage the aggregate.

参数

function_name

The name of the function used in SQL statements.

step_func

Callback function called for each row of the result set. Your PHP function should accumulate the result and store it in the aggregation context.

This function need to be defined as:

step(
    mixed $context,
    int $rownumber,
    mixed $value,
    mixed ...$values
): mixed

context: null for the first row; on subsequent rows it will have the value that was previously returned from the step function; you should use this to maintain the aggregate state.
rownumber: The current row number.
value: The first argument passed to the aggregate.
values: Further arguments passed to the aggregate.

The return value of this function will be used as the context argument in the next call of the step or finalize functions.

finalize_func

Callback function to aggregate the "stepped" data from each row. Once all the rows have been processed, this function will be called and it should then take the data from the aggregation context and return the result. This callback function should return a type understood by SQLite (i.e. scalar type).

This function need to be defined as:

fini(mixed $context, int $rowcount): mixed

context: Holds the return value from the very last call to the step function.
rowcount: Holds the number of rows over which the aggregate was performed.

The return value of this function will be used as the return value for the aggregate.

num_args

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

返回值

成功时返回 true，或者在失败时返回 false。

范例

示例 #1 max_length aggregation function example


<?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, $rownumber, $string) 
{
    if (strlen($string) > $context) {
        $context = strlen($string);
    }
    return $context;
}

function max_len_finalize($context, $rowcount) 
{
    return $context === null ? 0 : $context;
}

$db->sqliteCreateAggregate('max_len', 'max_len_step', 'max_len_finalize');

var_dump($db->query('SELECT max_len(a) from strings')->fetchAll());

?>

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 max_len_step function is called and passed a $context 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 $string has a length longer than the current maximum, we update the context to hold this new maximum length.

After all of the rows have been processed, SQLite calls the max_len_finalize function to determine the aggregate result. Here, we could perform some kind of calculation based on the data found in the $context. In our simple example though, we have been calculating the result as the query progressed, so we simply need to return the context value.

小技巧

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.

小技巧

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

参见

PDO::sqliteCreateFunction
sqlite_create_function()
sqlite_create_aggregate()

add a note

User Contributed Notes

There are no user contributed notes for this page.

官方地址：https://www.php.net/manual/en/pdo.sqlitecreateaggregate.php

有任何技术问题请点击这里网站运营推广招聘

IT PHP 编程语言 Linux 开发编程科技 Elasticsearch HTML/CSS/XML 网络 JAVA NoSQL 数据库面试 C/C++ Golang Git 算法操作系统正则表达式 Redis 互联网 MySql JavaScript 运维软件国际架构设计 Mac OS TCP/IP Excel Vim Windows Socket Oracle VR MongoDB Python 运营 MemCache 商业硬件电子娱乐设计 nginx 摄影游戏 WordPress HTTP 团建数码电器

php7 安装fileinfo扩展 preg_split — 通过一个正则表达式分隔字符串 php位值,解决 PHP 中 usort 在值相同时改变原始位置的问题 [PHP] inet_pton/inet_ntop IP地址转换函数 array_multisort() 多字段排序 PHPMailer设置utf8 PHPMailer字符集CharSet ADORecordSet对象 adodb手册 PHP 8.1 [鸟哥]PHP_INT_MIN 和 -9223372036854775808 opcache预加载 Composer的Packagist资源 mysql面试题 [鸟哥]PHP FFI详解 - 一种全新的PHP扩展方式 PHP7添加redis扩展 PHP mkdir()写出来的权限与mode值不符合 Packagist / Composer 中国全量镜像常用的php ADODB使用方法集锦 [原创]诡异的php-fpm超时问题 php中几种注释规范

略微加速

PHP官方手册 - 互联网笔记

PDO::sqliteCreateAggregate

说明

参数

返回值

范例

参见

User Contributed Notes