Analysis of common usage of PHP query statements

PHP is a scripting language widely used in website development. Querying data is a common task when performing database operations. This article will analyze the common usage of query statements in PHP through specific code examples to help readers better master PHP database operation skills.

1. Query using the mysqli extension

Mysqli is an extension in PHP used to operate the MySQL database. Database connections and data operations can be easily performed through the mysqli extension. The following is a simple example that demonstrates how to use mysqli for query operations:

<?php
// 连接数据库
$mysqli = new mysqli("localhost", "username", "password", "database");

// 检查数据库连接是否成功
if ($mysqli->connect_error) {
    die("数据库连接失败: " . $mysqli->connect_error);
}

// 查询数据
$query = "SELECT * FROM users";
$result = $mysqli->query($query);

// 处理查询结果
if ($result->num_rows > 0) {
    while($row = $result->fetch_assoc()) {
        echo "ID: " . $row["id"] . " - 姓名: " . $row["name"] . "<br>";
    }
} else {
    echo "没有查询到数据";
}

// 关闭数据库连接
$mysqli->close();
?>

In the above example, the database connection is first made through the constructor of the mysqli class, and then the query statement is executed and the query results are processed. Finally close the database connection. This is a simple query example that readers can expand and modify according to actual needs.

2. Query using PDO extension

In addition to the mysqli extension, there is also a PDO extension in PHP for database operations. PDO provides more flexible and secure database operations. interface. The following is an example of using PDO for query operations:

<?php
// 连接数据库
$dsn = "mysql:host=localhost;dbname=database";
$username = "username";
$password = "password";

try {
    $pdo = new PDO($dsn, $username, $password);
    $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

    // 查询数据
    $query = "SELECT * FROM users";
    $stmt = $pdo->query($query);

    // 处理查询结果
    while ($row = $stmt->fetch(PDO::FETCH_ASSOC)) {
        echo "ID: " . $row['id'] . " - 姓名: " . $row['name'] . "<br>";
    }
} catch (PDOException $e) {
    die("查询失败: " . $e->getMessage());
}

// 关闭数据库连接
$pdo = null;
?>

In the above example, the database connection is first made through the constructor of the PDO class, then the query statement is executed and the query results are processed, and finally the database connection is closed. . PDO provides a more convenient and secure data operation method, which can effectively prevent security issues such as SQL injection.

3. Query data and use prepared statements

In order to prevent security issues such as SQL injection, it is recommended to use prepared statements when performing query operations. The following is an example of using prepared statements for query operations:

<?php
// 连接数据库
$pdo = new PDO("mysql:host=localhost;dbname=database", "username", "password");

// 准备查询
$query = "SELECT * FROM users WHERE id = :id";
$stmt = $pdo->prepare($query);

// 绑定参数
$id = 1;
$stmt->bindParam(':id', $id, PDO::PARAM_INT);

// 执行查询
$stmt->execute();

// 处理查询结果
while ($row = $stmt->fetch(PDO::FETCH_ASSOC)) {
    echo "ID: " . $row['id'] . " - 姓名: " . $row['name'] . "<br>";
}

// 关闭数据库连接
$pdo = null;
?>

In the above example, first use the prepare method to prepare the query statement, then use the bindParam method to bind parameters, and finally execute the query and process the query results. Using prepared statements can effectively prevent SQL injection and improve the security of query operations.

Through the above examples, readers can have an in-depth understanding of the common usage of query statements in PHP, and make corresponding expansions and modifications according to actual needs. When performing database operations, security and efficiency are very important considerations, so it is recommended to fully consider data security and performance optimization when writing query statements. I hope this article will be helpful to readers in PHP database operations.

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