如何使用返回值的PDO_SQLSRV从PHP调用SQL Server存储过程？

$serverName = "server_name";
$connectionOptions = array(
    "Database" => "database_name",
    "Uid" => "username",
    "PWD" => "password"
);

$conn = new PDO("sqlsrv:Server=$serverName;Database=database_name", $connectionOptions);

$sql = "EXEC stored_procedure_name @param1 = ?, @param2 = ?";
$stmt = $conn->prepare($sql);

$param1 = 'value1';
$param2 = 'value2';

$stmt->bindParam(1, $param1, PDO::PARAM_STR);
$stmt->bindParam(2, $param2, PDO::PARAM_STR);

$stmt->execute();

// 获取返回值
$returnValue = null;
do {
    $row = $stmt->fetch(PDO::FETCH_ASSOC);
    if ($row) {
        $returnValue = $row['returnValue'];
    }
} while ($stmt->nextRowset());

echo "返回值：" . $returnValue;