Getting Started with PHP: Database Connections

PHP is a commonly used server-side scripting language that is widely used in the field of web development. Among them, interaction with the database is an important application scenario of PHP. This article will introduce how to connect to the database in PHP.

1. Basic concepts of database connection

In Web applications, relational databases are generally used to store and manage various data. In PHP applications, database connection refers to establishing a connection between a PHP application and a database through code to perform operations such as adding, deleting, modifying, and checking data. This process usually includes the following steps:

1. Choose a database that suits you: Currently, the more popular databases include MySQL, Oracle, PostgreSQL, etc. We need to choose the one that suits us best based on actual needs. database.
2. Determine the connection method: PHP can connect to the database in a variety of ways. In this article, we mainly introduce two commonly used database connection methods: MySQLi and PDO.
3. Determine connection parameters: Each connection method requires specifying the necessary parameters for the connection, such as host address, user name, password, database name, etc.

2. MySQLi connection

MySQLi is an extension officially recommended by PHP for interacting with the MySQL database. New versions of PHP have the MySQLi extension installed by default.

1. Establishing a connection

MySQLi provides a mysqli class to operate the MySQL database. First, you need to establish a connection with the database through the constructor of the mysqli class. Commonly used constructor parameters are as follows:

• host: server address, default is localhost.
• username: username.
• password: Password.
• dbname: The name of the database connected to by default.

The sample code is as follows:

//连接数据库
$mysqli = new mysqli('localhost', 'username', 'password', 'dbname');
//错误检查
if(mysqli_connect_errno()) {
    printf("Connect failed: %s
", mysqli_connect_error());
    exit();
}

2. Execute SQL statements

After the connection is successful, you can execute various SQL statements. MySQLi provides multiple methods to execute SQL statements, such as query, prepare, bind_param, execute, fetch, etc. Among them, the query method is used to execute simple SQL statements and return query results. The sample code is as follows:

//查询语句
$query = "SELECT * FROM users";
//执行查询
$result = $mysqli->query($query);
//遍历结果
while ($row = $result->fetch_assoc()) {
    echo $row['username'] . '<br />';
}

3. Close the connection

After all database operations are completed, it needs to be closed Database Connectivity.

//关闭连接
$mysqli->close();

2. PDO connection

PDO (PHP Data Objects) is a general object-based database operation method provided by PHP. It can not only interact with relational databases such as MySQL, but also support non- Relational Database.

1. Establishing a connection

PDO establishes a connection with the database through the PDO object. Commonly used constructor parameters are as follows:

• dsn: data source name, identifying database type, host address, database name, character set and other information.
• username: username.
• password: Password.
  The sample code is as follows:

//数据源名称
$dsn = 'mysql:host=localhost;port=3306;dbname=test;charset=utf8';
//连接数据库
try {
    $pdo = new PDO($dsn, 'username', 'password');
    //设置错误模式
    $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
 } catch (PDOException $e) {
    echo 'Connection failed: ' . $e->getMessage();
}

2. Execute SQL statements

PDO can preprocess SQL statements to avoid SQL injection attacks and improve execution efficiency. Prepared statements usually contain three steps:

1. Prepare prepared statements.
2. Bind parameters.
3. Execute prepared statements.

The sample code is as follows:

//预处理语句
$stmt = $pdo->prepare("SELECT * FROM users WHERE id=:id");
//绑定参数
$id = 1;
$stmt->bindParam(':id', $id, PDO::PARAM_INT);
//执行预处理语句
$stmt->execute();
//遍历结果
while ($row = $stmt->fetch(PDO::FETCH_ASSOC)) {
    echo $row['username'] . '<br />';
}

3. Close the connection

After all database operations are completed, the database connection needs to be closed.

//关闭连接
$pdo = null;

3. Suggestions and Precautions

1. It is recommended to use PDO to connect to the database, because it supports multiple types of databases and provides better code readability and security. sex.
2. It is recommended to use preprocessed SQL statements to avoid SQL injection attacks and improve execution efficiency.
3. Pay attention to the security of database connections and try to avoid storing important information such as user names and passwords in plain text in the code.
4. Pay attention to closing the database connection in time to avoid resource waste and security risks.

Summary: This article introduces two common ways to interact with MySQL database in PHP, namely MySQLi and PDO. Through the introduction of this article, readers can learn how to establish a connection with the MySQL database and execute various SQL statements. In actual development, in order to ensure the security, maintainability and scalability of the application, it is recommended to use PDO to connect to the MySQL database and use prepared statements to execute SQL statements.

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