How to Connect to a Database Using PHP

Using PHP to Connect to Database

Introduction

Connecting to a database in PHP is a fundamental task when developing web applications. This article will guide you step‑by‑step through the process required to connect PHP to various types of databases.

Establish Connection

To establish a database connection, you can use the following code:

$servername = "localhost";
$username = "username";
$password = "password";
$database = "dbname";

// Create connection
$conn = new mysqli($servername, $username, $password, $database);

// Check connection
if ($conn->connect_error) {
    die("连接失败: " . $conn->connect_error);
}

echo "成功连接到数据库";

Using PDO

PDO (PHP Data Objects) is a more powerful connection method that provides a unified interface for different database types. There are three ways to create a PDO connection:

1. Object‑oriented style

$host = "localhost";
$port = "3306"; // MySQL default port
$dbname = "dbname";
$username = "username";
$password = "password";

$dsn = "mysql:dbname=$dbname;host=$host;charset=UTF8;port=$port";

try {
    // Create connection
    $conn = new PDO($dsn, $username, $password);
    // Set error mode
    $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    echo "成功连接到数据库";
} catch (PDOException $e) {
    echo "连接失败: " . $e->getMessage();
}

2. Using PDOStatement

$host = "localhost";
$database = "dbname";
$username = "username";
$password = "password";

// Create connection
$conn = new PDO("mysql:host=$host;dbname=$database", $username, $password);

// Prepare statement
$stmt = $conn->prepare("SELECT * FROM users");
$stmt->execute();

// Iterate results
while ($result = $stmt->fetch(PDO::FETCH_ASSOC)) {
    echo "ID: " . $result['id'] . ", 名称: " . $result['name'] . "
";
}

3. Shortcut method

$dsn = "mysql:dbname=mydb;host=localhost";
$conn = new PDO($dsn, $username, $password);
// Practical example: retrieve user by userId
$userId = 1;

// Query statement
$stmt = $conn->prepare("SELECT * FROM users WHERE id = ?");
$stmt->bind_param("i", $userId); // i indicates integer
$stmt->execute();

// Get result
$result = $stmt->get_result();

if ($row = $result->fetch_assoc()) {
    echo "名称: " . $row['name'] . "
";
    echo "电子邮件: " . $row['email'] . "
";
} else {
    echo "没有找到用户";
}

Close Connection

After completing database operations, be sure to close the connection to free resources:

$conn->close();