php连接sqlserver五种方法是什么

$server = 'localhost';
$username = 'sa';
$password = '';
$database = 'example_db';
$conn = mssql_connect($server, $username, $password);
mssql_select_db($database, $conn);

$server = 'localhost';
$username = 'sa';
$password = '';
$database = 'example_db';
$conn = sqlsrv_connect($server, array('UID'=>$username, 'PWD'=>$password, 'Database'=>$database));

$server = 'localhost';
$username = 'sa';
$password = '';
$database = 'example_db';
try {
    $conn = new PDO("sqlsrv:Server=$server;Database=$database", $username, $password);
}
catch(PDOException $e) {
    die("Error connecting to SQL Server: " . $e->getMessage());
}

$dsn = 'Driver={SQL Server};Server=localhost;Database=example_db';
$username = 'sa';
$password = '';
$conn = odbc_connect($dsn, $username, $password);

$conn = new COM('ADODB.Connection');
$dsn = 'Driver={SQL Server};Server=localhost;Database=example_db';
$conn->Open($dsn, 'sa', '');