An explanation of how PHP performs database operations and prevents page timeouts and automatically refreshes pages

It is very common to operate the database in PHP development. If we stay on a page for a long time without operating, there will be prompts or errors. I believe everyone has encountered it. So today we will talk about how to operate the database. Take action and prevent page timeouts!

Instructions:

When initializing or modifying the database:
1. Simply use sql statements directly Finish.
2. A little more complicated, it can be completed by executing php code (read data and then write/modify data).

When using php code (not command line), we may encounter web page timeout. There are generally three solutions:
1. Set php.ini:

max_execution_time

2. Add in the code:

set_time_limit(0);  
//0表示不超时

3. The page refreshes automatically and completes the entire work in batches:
The page can change with the execution process, such as dynamically telling the user how far it has been executed, instead of waiting for a single page.
Below, we mainly sort out the third method.

The page automatically refreshes:

Page refreshThe page jumps and stops jumping when a certain condition is met.
Page jump: Output meta tags to achieve

if ($flag) {
    //跳转页面，xxx为该php文件的文件名
    echo &#39;<meta http-equiv="refresh" content="0;url=xxx.php?">&#39;;
} else {
    //刷新停止
}

Refresh and pass parameters at the same time to control database operations:

In the meta url, we can use Get way to pass a parameter.
This parameter can be used to change the limit of the SQL statement to implement a part of the function each time.

$page = isset($_GET['page']) ? $_GET['page'] : 0;
//用$page构造sql语句或其它功能
//数据库操作或其它功能
//设置$flag
$flag = $pdostatement->rowCount() == 0;  //比如数据库影响行数
//决定 跳转刷新 或 停止
if ($flag) {
    //跳转页面，xxx为该php文件的文件名
    echo &#39;<meta http-equiv="refresh" content="0;url=xxx.php?page=&#39; . ++$page . &#39;">&#39;;
} else {
    //刷新停止
}

Suppose, +1 for a certain field data, specific implementation:

I am not very familiar with SQL now.
If it is just a limit limit, it may happen that the data that has been queried is queried again and executed a second time?
Personally, it is best to add the order of the primary key by

<meta charset="UTF-8">
<?php
$page = isset($_GET[&#39;page&#39;]) ? $_GET[&#39;page&#39;] : 0;
$step = 50;  //每次刷新更新 50条数据
$limit_start = $page * 50;

$dsn = "mysql:host=localhost;dbname=db_name";
try {
    $pdo = new PDO($dsn, "root", "123456");
    $sql = <<<SQL
SELECT col_num, col_id
FROM table_name
ORDER by col_id
LIMIT {$limit_start},{$step}
SQL;
    $pdostatement = $pdo->prepare($sql);
    $pdostatement->execute();
    $pdostatement->setFetchMode(PDO::FETCH_NUM);
    $num = $pdostatement->rowCount();

    if ($num == 0) {
        echo "sql执行完毕";
    } else {
        echo "正在执行sql<br>";

        $sql_update = "UPDATE table_name ";
        while (list($col_num, $col_id) = $pdostatement->fetch(PDO::FETCH_NUM)) {
            $col_name++;
            $sql_update .= <<<SQL
SET col_name = "{$col_num}"
WHERE col_id = "{$col_id}" , 
SQL;
        }
        $sql_update = substr($sql_update, 0, -1);  //去掉最后的逗号
  $pdostatement_update = $pdo->prepare($sql_update);
        $pdostatement_update->execute();
        $num_update = $pdostatement_update->rowCount();
        if ($num_update == 0) {
            echo $gfc_id . "修改出错，停止更新";
        } else {
            echo &#39;<meta http-equiv="refresh" content="0;url=jianshu.php?page=&#39; . (++$page) . &#39;">&#39;;
        }
    }
} catch (PDOException $e) {
    echo "数据库连接失败" . $e->getMessage();  //连接失败，获取错误信息
  exit;
}

The above is how PHP performs database operations and prevents page timeouts and automatically refreshes the page. These methods are used in our PHP development. What is used for a long time is also very popular.

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