phpmysql选择数据库代码

<?php
// 创建连接
$conn = new mysqli("localhost", "username", "password", "database_name");

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

// 选择数据库
$db_selected = mysqli_select_db($conn, "database_name");

if (!$db_selected) {
    die("选择数据库失败: " . mysqli_error($conn));
}

echo "数据库选择成功";

// 关闭连接
$conn->close();
?>

<?php
try {
    // 创建PDO实例
    $conn = new PDO("mysql:host=localhost;dbname=database_name", "username", "password");

    // 设置PDO错误模式为异常
    $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

    echo "数据库连接成功";
} catch(PDOException $e) {
    echo "数据库连接失败: " . $e->getMessage();
}

// 关闭连接
$conn = null;
?>