MySQL How-To Guide in PHP

PHP is one of the most commonly used programming languages ​​in web development, while MySQL is one of the most popular relational database management systems. During web application development, one of the main functions of PHP is to interact with the MySQL database to store and retrieve data. This article will provide you with a basic MySQL operation guide to help you easily perform database programming in PHP.

1. Connecting to a MySQL database
   In PHP, you can use MySQLi or PDO extensions to connect to a MySQL database. The following are connection examples for both extensions:

//连接MySQLi扩展
$mysqli = new mysqli('localhost', '用户名', '密码', '数据库名');

//连接PDO扩展
$pdo = new PDO('mysql:host=localhost;dbname=数据库名', '用户名', '密码');

2. Execute SQL query statements
   After connecting to the database, you can use PHP to run various MySQL commands. Here are some common SQL query examples:

//选择一个数据表中的所有记录
$result = $mysqli->query('SELECT * FROM 表名');

//查询一个数据表中的记录计数
$count = $pdo->query('SELECT COUNT(*) FROM 表名')->fetchColumn();

//插入一条新记录到数据表中
$mysqli->query('INSERT INTO 表名 (字段值1, 字段值2) VALUES ("值1", "值2")');

//更新一个数据表的记录
$pdo->query('UPDATE 表名 SET 字段 = "新值" WHERE 条件');

3. Processing Query Results
   Once you run a query, you need to be able to read the returned data. Here is some sample code that demonstrates how to handle query results:

//循环遍历每个结果行，并打印其中的每一列
while ($row = $result->fetch_assoc()) {
    echo $row['字段名1'] . ' | ' . $row['字段名2'] . '<br>';
}

//将查询结果中的第一列（即第一个字段）存储在一个数组中
$column_values = $pdo->query('SELECT 字段名 FROM 表名')->fetchAll(PDO::FETCH_COLUMN, 0);

4. Error handling
   When you use PHP to connect to MySQL and execute a SQL query, various errors may occur. Here are some common error handling methods:

//使用MySQLi扩展
if ($mysqli->connect_errno) {
    die('连接错误: ' . $mysqli->connect_error);
}
if (!$mysqli->query('SELECT * FROM 表名')) {
    die('查询错误：' . $mysqli->error);
}

//使用PDO扩展
if (!$pdo) {
    die('连接错误: ' . print_r($pdo->errorInfo(), true));
}
if (!$pdo->query('SELECT * FROM 表名')) {
    die('查询错误：' . print_r($pdo->errorInfo(), true));
}

5. Database Security
   Security is very important when doing database programming. Here are some basic security tips:

a. Never trust user input.
b. Use prepared statements or PDO prepare statements appropriately to avoid SQL injection attacks.
c. Use PHP password hash functions (such as password_hash() and password_verify()) to encrypt sensitive information stored in the database.

Summary
In this article, we have provided a basic MySQL how-to guide to help you interact with a MySQL database in PHP. This helps you build powerful web applications more easily and keeps your database and its contents secure. This guide is just a basic reference, you should also have a deep understanding of MySQL and PHP.

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