Summary of database connection technology and common problems in PHP

PHP is an open source language used for processing data from dynamic web applications. Many web applications use databases to store and process data. Database connections are an inevitable part of developing web applications. In this article, we will discuss database connection technology in PHP and a summary of common problems.

1. MySQLi vs PDO

In PHP, there are two database connection technologies available: MySQLi and PDO. MySQLi is an enhanced version of MySQL extension, supporting more features and faster speed, while PDO can be used for multiple databases, such as MySQL, Oracle and SQL Server.

MySQLi uses object-oriented programming (OOP) and procedure-oriented programming (POP) structures. It provides object-oriented API and command line (CLI) procedures. MySQLi can also handle advanced application scenarios such as transactions and stored procedures, making it one of the most common ways for PHP to connect to MySQL. Here is an example of using MySQLi to connect to a MySQL database:

// 配置数据库连接信息
$host = 'localhost';
$username = 'user';
$password = 'pwd';
$dbname = 'test_db';

// 连接MySQL数据库
$conn = mysqli_connect($host, $username, $password, $dbname);

// 检查连接是否成功
if (!$conn) {
    die("连接失败: " . mysqli_connect_error());
}
echo "连接成功";

PDO separates the database driver from the PDO class. This means you can easily change the database and leave the code in place. PDO also includes many database abstraction layers, including prepared statements and transactions. The following is an example of using PDO to connect to a MySQL database:

// 配置数据库连接信息
$host = 'localhost';
$username = 'user';
$password = 'pwd';
$dbname = 'test_db';

// 连接MySQL数据库
try {
    $conn = new PDO("mysql:host=$host;dbname=$dbname", $username, $password);
    // 设置 PDO 错误模式为异常
    $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    echo "连接成功";
} catch(PDOException $e) {
    echo "连接失败: " . $e->getMessage();
}

2. Common problems and solutions

Common problems may occur when using database connections in PHP. The following are some best practices to solve these problems:

(1) Encoding issue

Before connecting to the database, the encoding must be set. In MySQLi, you can use mysqli_set_charset() to set the encoding; in PDO, you can set the encoding when connecting to the database. The following is an example:

// 在MySQLi中设置编码
mysqli_set_charset($conn,"utf8");

// 在PDO中设置编码
$conn->exec("set names utf8");

(2) SQL injection

When users enter data, malicious code may be constructed to conduct SQL injection attacks. To prevent this from happening, you should use prepared statements. The following is an example of using prepared statements:

// 使用MySQLi中预处理语句来查询数据
$stmt = $conn->prepare("SELECT * FROM users WHERE username = ? AND password = ?");
$stmt->bind_param("ss", $username, $password);

// 使用PDO中预处理语句来查询数据
$stmt = $conn->prepare("SELECT * FROM users WHERE username = :username AND password = :password");
$stmt->bindParam(':username', $username);
$stmt->bindParam(':password', $password);
$stmt->execute();

(3) Open too many connections

If too many connections are opened at the same time, it may cause the server to crash. To prevent this from happening, you can use connection pooling. Connection pooling helps you manage connections and clear idle connections regularly. The following is an example of using a connection pool:

// 创建连接池并设置最大连接数以及空闲时间
$pool = new ConnectionPool('mysql:host=localhost;dbname=test_db', 'user', 'pwd', [
    'max_connections' => 10,
    'idle_timeout' => 30,
]);

// 从连接池中取出连接
$conn = $pool->getConnection();

// 将连接放回连接池
$pool->release($conn);

In short, in PHP, connecting to the database is very important. MySQLi and PDO are two commonly used methods to connect to databases, and you should choose carefully before using them. At the same time, you need to pay attention to common problems when using it, such as encoding problems, SQL injection and opening too many connections.

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