pdo连接odbc

Question

/*$conn=odbc_connect('MsSql8','ccy','123456');$sql='select * from cj_users where userid_int = 2412';$exec=odbc_exec($conn,$sql);//执行语句while(odbc_fetch_array($exec)){$abc=odbc_result($exec,'uname');echo $abc;}*/按照这个方法是可以正常连接的，也有数据返回为什么用pdo这个方法会报错$type = 'odbc'; $db_name = 'MsSql8';$host = '127.0.0.1';$username = 'ccy';$password = '123456';$dsn = "$type:host=$host;dbname=$db_name";try {$pdo = new PDO($dsn, $username, $password); } catch (Exception $e) {die($e->getMessage()); }输出的结果是SQLSTATE[IM002] SQLDriverConnect: 0 [Microsoft][ODBC 驱动程序管理器] 未发现数据源名称并且未指定默认驱动程序