实战案例：使用 PHP 连接到异构数据库系统

* PDO_SQLSRV：用于连接到 Microsoft SQL Server
* PDO_OCI：用于连接到 Oracle 数据库
* PDO_MYSQL：用于连接到 MySQL 数据库

$dsn = 'sqlsrv:Server=myServer;Database=myDB';
$user = 'myUser';
$password = 'myPassword';

try {
    $conn = new PDO($dsn, $user, $password);
} catch (PDOException $e) {
    echo '连接失败: ' . $e->getMessage();
}

// 连接到 SQL Server 数据库
$dsn = 'sqlsrv:Server=myServer;Database=myDB';
$user = 'myUser';
$password = 'myPassword';
$conn1 = new PDO($dsn, $user, $password);

// 查询 SQL Server 数据
$query1 = 'SELECT * FROM Customers';
$stmt1 = $conn1->prepare($query1);
$stmt1->execute();
$customers1 = $stmt1->fetchAll();

// 连接到 Oracle 数据库
$dsn = 'oci:dbname=//myOracleServer/myDB';
$user = 'myUser';
$password = 'myPassword';
$conn2 = new PDO($dsn, $user, $password);

// 查询 Oracle 数据
$query2 = 'SELECT * FROM Employees';
$stmt2 = $conn2->prepare($query2);
$stmt2->execute();
$employees2 = $stmt2->fetchAll();

// 合并两组数据
$data = array_merge($customers1, $employees2);

// 显示结果
echo '<ul>';
foreach ($data as $row) {
    echo '<li>' . $row['Name'] . '</li>';
}
echo '</ul>';